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This document describes the structure, content, construction, and semantics of language tags for use in cases where it is desirable to indicate the language used in an information object. It also describes how to register values for use in language tags and the creation of user-defined extensions for private interchange.
2. The Language Tag
2.1. Syntax
2.2. Language Subtag Sources and Interpretation
2.2.1. Primary Language Subtag
2.2.2. Extended Language Subtags
2.2.3. Script Subtag
2.2.4. Region Subtag
2.2.5. Variant Subtags
2.2.6. Extension Subtags
2.2.7. Private Use Subtags
2.2.8. Grandfathered Registrations
2.2.9. Classes of Conformance
3. Registry Format and Maintenance
3.1. Format of the IANA Language Subtag Registry
3.1.1. File Format
3.1.2. Record Definitions
3.1.3. Subtag and Tag Fields
3.1.4. Description Field
3.1.5. Deprecated Field
3.1.6. Preferred-Value Field
3.1.7. Prefix Field
3.1.8. Suppress-Script Field
3.1.9. Macrolanguage Field
3.1.10. Comments Field
3.2. Language Subtag Reviewer
3.3. Maintenance of the Registry
3.4. Stability of IANA Registry Entries
3.5. Registration Procedure for Subtags
3.6. Possibilities for Registration
3.7. Extensions and the Extensions Registry
3.8. Update of the Language Subtag Registry
4. Formation and Processing of Language Tags
4.1. Choice of Language Tag
4.2. Meaning of the Language Tag
4.3. Length Considerations
4.3.1. Working with Limited Buffer Sizes
4.3.2. Truncation of Language Tags
4.4. Canonicalization of Language Tags
4.5. Considerations for Private Use Subtags
5. IANA Considerations
5.1. Language Subtag Registry
5.2. Extensions Registry
6. Security Considerations
7. Character Set Considerations
8. Changes from RFC 4646
9. References
9.1. Normative References
9.2. Informative References
Appendix A. Acknowledgements
Appendix B. Examples of Language Tags (Informative)
Appendix C. Examples of Registration Forms
§ Authors' Addresses
§ Intellectual Property and Copyright Statements
Human beings on our planet have, past and present, used a number of languages. There are many reasons why one would want to identify the language used when presenting or requesting information.
A user's language preferences often need to be identified so that appropriate processing can be applied. For example, the user's language preferences in a Web browser can be used to select Web pages appropriately. Language preferences can also be used to select among tools (such as dictionaries) to assist in the processing or understanding of content in different languages.
In addition, knowledge about the particular language used by some piece of information content might be useful or even required by some types of processing; for example, spell-checking, computer-synthesized speech, Braille transcription, or high-quality print renderings.
One means of indicating the language used is by labeling the information content with an identifier or "tag". These tags can be used to specify user preferences when selecting information content, or for labeling additional attributes of content and associated resources.
Tags can also be used to indicate additional language attributes of content. For example, indicating specific information about the dialect, writing system, or orthography used in a document or resource may enable the user to obtain information in a form that they can understand, or it can be important in processing or rendering the given content into an appropriate form or style.
This document specifies a particular identifier mechanism (the language tag) and a registration function for values to be used to form tags. It also defines a mechanism for private use values and future extension.
This document replaces [RFC4646] (Phillips, A. and M. Davis, "Tags for Identifying Languages," September 2006.), which replaced [RFC3066] (Alvestrand, H., "Tags for the Identification of Languages," January 2001.) and its predecessor [RFC1766] (Alvestrand, H., "Tags for the Identification of Languages," March 1995.). For a list of changes in this document, see Section 8 (Changes from RFC 4646).
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [RFC2119] (Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels," March 1997.).
Language tags are used to help identify languages, whether spoken, written, signed, or otherwise signaled, for the purpose of communication. This includes constructed and artificial languages, but excludes languages not intended primarily for human communication, such as programming languages.
The language tag is composed of one or more parts, known as "subtags". Each subtag consists of a sequence of alphanumeric characters. Subtags are distinguished and separated from one another by a hyphen ("-", ABNF [RFC5234] (Crocker, D. and P. Overell, "Augmented BNF for Syntax Specifications: ABNF," January 2008.) %x2D). Usually a language tag contains a "primary language" subtag, followed by a (possibly empty) series of subsequent subtags, each of which refines or narrows the range of languages identified by the overall tag.
Most subtags are distinguished by length, position in the tag, and content: subtags can be recognized solely by these features. This makes it possible to construct a parser that can extract and assign some semantic information to the subtags, even if the specific subtag values are not recognized. Thus, a parser need not have a list of valid tags or subtags (that is, a copy of some version of the IANA Language Subtag Registry) in order to perform common searching and matching operations. The grandfathered tags registered under RFC 3066 (Alvestrand, H., "Tags for the Identification of Languages," January 2001.) [RFC3066], a fixed list that can never change, are the only exception to this ability to infer meaning from subtag structure.
The syntax of the language tag in ABNF [RFC5234] (Crocker, D. and P. Overell, "Augmented BNF for Syntax Specifications: ABNF," January 2008.) is:
Language-Tag = langtag / privateuse ; private use tag / irregular ; tags grandfathered by rule langtag = (language ["-" script] ["-" region] *("-" variant) *("-" extension) ["-" privateuse]) language = 2*3ALPHA ; shortest ISO 639 code / 4ALPHA ; reserved for future use / 5*8ALPHA ; registered language subtag script = 4ALPHA ; ISO 15924 code region = 2ALPHA ; ISO 3166-1 code / 3DIGIT ; UN M.49 code variant = 5*8alphanum ; registered variants / (DIGIT 3alphanum) extension = singleton 1*("-" (2*8alphanum)) singleton = %x41-57 / %x59-5A / %x61-77 / %x79-7A / DIGIT ; "a"-"w" / "y"-"z" / "A"-"W" / "Y"-"Z" / "0"-"9" ; Single alphanumerics ; "x" is reserved for private use privateuse = "x" 1*("-" (1*8alphanum)) irregular = "en-GB-oed" / "i-ami" / "i-bnn" / "i-default" / "i-enochian" / "i-hak" / "i-klingon" / "i-lux" / "i-mingo" / "i-navajo" / "i-pwn" / "i-tao" / "i-tay" / "i-tsu" / "no-bok" / "no-nyn" / "sgn-BE-FR" / "sgn-BE-NL" / "sgn-CH-DE" / "zh-cmn" / "zh-cmn-Hans" / "zh-cmn-Hant" / "zh-gan" / "zh-min" / "zh-min-nan" / "zh-wuu" / "zh-yue" alphanum = (ALPHA / DIGIT) ; letters and numbers
| Figure 1: Language Tag ABNF
All subtags have a maximum length of eight characters and whitespace is not permitted in a language tag. There is a subtlety in the ABNF production 'variant': variants starting with a digit MAY be four characters long, while those starting with a letter MUST be at least five characters long. For examples of language tags, see Appendix B (Examples of Language Tags (Informative)).
Note Well: the ABNF syntax does not distinguish between upper and lowercase. The appearance of upper and lowercase letters in the various ABNF productions above do not affect how implementations interpret tags. That is, the tag "I-AMI" matches the item "i-ami" in the 'irregular' production. At all times, the tags and their subtags, including private use and extensions, are to be treated as case insensitive: there exist conventions for the capitalization of some of the subtags, but these MUST NOT be taken to carry meaning.
For example:
However, in the tags defined by this document, the uppercase US-ASCII letters in the range 'A' through 'Z' are considered equivalent and mapped directly to their US-ASCII lowercase equivalents in the range 'a' through 'z'. Thus, the tag "mn-Cyrl-MN" is not distinct from "MN-cYRL-mn" or "mN-cYrL-Mn" (or any other combination), and each of these variations conveys the same meaning: Mongolian written in the Cyrillic script as used in Mongolia.
Although case distinctions do not carry meaning in language tags, consistent formatting and presentation of the tags will aid users. The format of the tags and subtags in the registry is RECOMMENDED. In this format, all subtags, including all those following singletons (that is, in extension or private-use sequences) are in lowercase. The exceptions to this are: all other non-initial two-letter subtags are uppercase and all other non-initial four-letter subtags are titlecase.
Note that although [RFC5234] (Crocker, D. and P. Overell, "Augmented BNF for Syntax Specifications: ABNF," January 2008.) refers to octets, the language tags described in this document are sequences of characters from the US-ASCII [ISO646] (International Organization for Standardization, "ISO/IEC 646:1991, Information technology -- ISO 7-bit coded character set for information interchange.," 1991.) repertoire. Language tags MAY be used in documents and applications that use other encodings, so long as these encompass the US-ASCII repertoire. An example of this would be an XML document that uses the UTF-16LE [RFC2781] (Hoffman, P. and F. Yergeau, "UTF-16, an encoding of ISO 10646," February 2000.) encoding of [Unicode] (Unicode Consortium, "The Unicode Consortium. The Unicode Standard, Version 5.0, (Boston, MA, Addison-Wesley, 2003. ISBN 0-321-49081-0)," January 2007.).
The namespace of language tags and their subtags is administered by the Internet Assigned Numbers Authority (IANA) [RFC2860] (Carpenter, B., Baker, F., and M. Roberts, "Memorandum of Understanding Concerning the Technical Work of the Internet Assigned Numbers Authority," June 2000.) according to the rules in Section 5 (IANA Considerations) of this document. The Language Subtag Registry maintained by IANA is the source for valid subtags: other standards referenced in this section provide the source material for that registry.
Terminology used in this document:
The definitions in this section apply to the various subtags within the language tags defined by this document, excepting those "grandfathered" tags defined in Section 2.2.8 (Grandfathered Registrations).
Language tags are designed so that each subtag type has unique length and content restrictions. These make identification of the subtag's type possible, even if the content of the subtag itself is unrecognized. This allows tags to be parsed and processed without reference to the latest version of the underlying standards or the IANA registry and makes the associated exception handling when parsing tags simpler.
Subtags in the IANA registry that do not come from an underlying standard can only appear in specific positions in a tag. Specifically, they can only occur as primary language subtags or as variant subtags.
Note that sequences of private use and extension subtags MUST occur at the end of the sequence of subtags and MUST NOT be interspersed with subtags defined elsewhere in this document.
Single-letter and single-digit subtags are reserved for current or future use. These include the following current uses:
The primary language subtag is the first subtag in a language tag (with the exception of private use and certain grandfathered tags) and cannot be omitted. The following rules apply to the primary language subtag:
Note: For languages that have both an ISO 639-1 two-character code and a three character code assigned by either ISO 639-2 or ISO 639-3, only the ISO 639-1 two-character code is defined in the IANA registry.
Note: For languages that have no ISO 639-1 two-character code and for which the ISO 639-2/T (Terminology) code and the ISO 639-2/B (Bibliographic) codes differ, only the Terminology code is defined in the IANA registry. At the time this document was created, all languages that had both kinds of three-character code were also assigned a two-character code; it is expected that future assignments of this nature will not occur.
Note: To avoid problems with versioning and subtag choice as experienced during the transition between RFC 1766 and RFC 3066, as well as the canonical nature of subtags defined by this document, the ISO 639 Registration Authority Joint Advisory Committee (ISO 639/RA-JAC) has included the following statement in [iso639.prin] (ISO 639 Joint Advisory Committee, "ISO 639 Joint Advisory Committee: Working principles for ISO 639 maintenance," March 2000.):
"A language code already in ISO 639-2 at the point of freezing ISO 639-1 shall not later be added to ISO 639-1. This is to ensure consistency in usage over time, since users are directed in Internet applications to employ the alpha-3 code when an alpha-2 code for that language is not available."
In order to avoid instability in the canonical form of tags, if a two-character code is added to ISO 639-1 for a language for which a three-character code was already included in either ISO 639-2 or ISO 639-3, the two-character code MUST NOT be registered. See Section 3.4 (Stability of IANA Registry Entries).
For example, if some content were tagged with 'haw' (Hawaiian), which currently has no two-character code, the tag would not be invalidated if ISO 639-1 were to assign a two-character code to the Hawaiian language at a later date.
Note: An example of independent primary language subtag registration might include: one of the grandfathered IANA registrations is "i-enochian". The subtag 'enochian' could be registered in the IANA registry as a primary language subtag (assuming that ISO 639 does not register this language first), making tags such as "enochian-AQ" and "enochian-Latn" valid.
[RFC4646] (Phillips, A. and M. Davis, "Tags for Identifying Languages," September 2006.) contained an additional type of subtag called the 'extended language subtag' to allow for certain kinds of compatibility mappings which ultimately were not used. These subtags were reserved for future use and ultimately removed from the ABNF. They MUST NOT be registered or used to form language tags. See also Section 2.2.9 (Classes of Conformance) for a discussion of the consequences of removing the 'extlang' production from grammar.
Note: a few grandfathered tags (Section 2.2.8 (Grandfathered Registrations)) matched the 'extlang' production in RFC 4646, and thus were not considered 'irregular'. These tags are still valid and were added to the 'irregular' production in the ABNF.
Script subtags are used to indicate the script or writing system variations that distinguish the written forms of a language or its dialects. The following rules apply to the script subtags:
Example: "sr-Latn" represents Serbian written using the Latin script.
Region subtags are used to indicate linguistic variations associated with or appropriate to a specific country, territory, or region. Typically, a region subtag is used to indicate regional dialects or usage, or region-specific spelling conventions. A region subtag can also be used to indicate that content is expressed in a way that is appropriate for use throughout a region, for instance, Spanish content tailored to be useful throughout Latin America.
The following rules apply to the region subtags:
- UN numeric codes assigned to 'macro-geographical (continental)' or sub-regions MUST be registered in the registry. These codes are not associated with an assigned ISO 3166-1 alpha-2 code and represent supra-national areas, usually covering more than one nation, state, province, or territory.
- UN numeric codes for 'economic groupings' or 'other groupings' MUST NOT be registered in the IANA registry and MUST NOT be used to form language tags.
- UN numeric codes for countries or areas which are assigned ISO 3166-1 alpha2 codes already present in the registry, MUST be defined according to the rules in Section 3.4 (Stability of IANA Registry Entries) and MUST be used to form language tags that represent the country or region for which they are defined. This happens when ISO 3166-1 reassigns a code already included in the registry and formerly used for one country to another.
- UN numeric codes for countries or areas for which there is an associated ISO 3166-1 alpha-2 code in the registry MUST NOT be entered into the registry and MUST NOT be used to form language tags. Note that the ISO 3166-based subtag in the registry MUST actually be associated with the UN M.49 code in question.
- UN numeric codes and ISO 3166-1 alpha-2 codes for countries or areas listed as eligible for registration in [RFC4645] (Ewell, D., "Initial Language Subtag Registry," September 2006.) but not presently registered MAY be entered into the IANA registry via the process described in Section 3.5 (Registration Procedure for Subtags). Once registered, these codes MAY be used to form language tags.
- All other UN numeric codes for countries or areas that do not have an associated ISO 3166-1 alpha-2 code MUST NOT be entered into the registry and MUST NOT be used to form language tags. For more information about these codes, see Section 3.4 (Stability of IANA Registry Entries).
"de-AT" represents German ('de') as used in Austria ('AT').
"sr-Latn-RS" represents Serbian ('sr') written using Latin script ('Latn') as used in Serbia ('RS').
"es-419" represents Spanish ('es') appropriate to the UN-defined Latin America and Caribbean region ('419').
Variant subtags are used to indicate additional, well-recognized variations that define a language or its dialects that are not covered by other available subtags. The following rules apply to the variant subtags:
Variant subtag records in the language subtag registry MAY include one or more 'Prefix' fields. The 'Prefix' indicates the language tag or tags that would make a suitable prefix (with other subtags, as appropriate) in forming a language tag with the variant. That is, each of the subtags in the prefix SHOULD appear, in order, before the variant. For example, the subtag 'nedis' has a Prefix of "sl", making it suitable for forming language tags such as "sl-nedis" and "sl-IT-nedis", but not suitable for use in a tag such as "zh-nedis" or "it-IT-nedis".
"sl-nedis" represents the Natisone or Nadiza dialect of Slovenian.
"de-CH-1996" represents German as used in Switzerland and as written using the spelling reform beginning in the year 1996 C.E.
Most variants that share a prefix are mutually exclusive. For example, the German orthographic variations '1996' and '1901' SHOULD NOT be used in the same tag, as they represent the dates of different spelling reforms. A variant that can meaningfully be used in combination with another variant SHOULD include a 'Prefix' field in its registry record that lists that other variant. For example, if another German variant 'example' were created that made sense to use with '1996', then 'example' should include two Prefix fields: "de" and "de-1996".
Extensions provide a mechanism for extending language tags for use in various applications. They are intended to identify information which is commonly used in association with languages or language tags, but which is not part of language identification. See Section 3.7 (Extensions and the Extensions Registry). The following rules apply to extensions:
For example, if the prefix singleton 'r' and the shown subtags were defined, then the following tag would be a valid example: "en-Latn-GB-boont-r-extended-sequence-x-private"
Private use subtags are used to indicate distinctions in language important in a given context by private agreement. The following rules apply to private use subtags:
For example: The Unicode Consortium defines a set of private use extensions in LDML ([UTS35] (Davis, M., "Unicode Technical Standard #35: Locale Data Markup Language (LDML)," December 2007.), Locale Data Markup Language, the Unicode standard for defining locale data) such as in the tag "es-419-x-ldml-collation-traditio", which indicates Latin American Spanish with traditional order for sorted lists.
Prior to RFC 4646, whole language tags were registered according to the rules in RFC 1766 and/or RFC 3066. These registered tags maintain their validity. Of those tags, those that were made obsolete or redundant by the advent of RFC 4646, by this document, or by subsequent registration of subtags are maintained in the registry in records as "redundant" records. Those tags that do not match the 'langtag' production in the ABNF in this document or that contain subtags that do not individually appear in the registry are maintained in the registry in records of the "grandfathered" type.
Grandfathered tags contain one or more subtags that are not defined in the Language Subtag Registry (see Section 3 (Registry Format and Maintenance)). Redundant tags consist entirely of subtags defined above and whose independent registration was superseded by [RFC4646] (Phillips, A. and M. Davis, "Tags for Identifying Languages," September 2006.). For more information see Section 3.8 (Update of the Language Subtag Registry).
Some grandfathered tags are "regular" in that they match the 'langtag' production in Figure 1 (Language Tag ABNF). In some cases, these tags could become redundant if their (currently unregistered) subtags were to be registered (as variants, for example). In other cases, although the subtags match the language tag pattern, the meaning assigned to the various subtags is prohibited by rules elsewhere in this document. Those tags can never become redundant.
The remaining grandfathered tags are "irregular" and do not match the 'langtag' production. These are listed in the 'irregular' production in Figure 1 (Language Tag ABNF). These grandfathered tags can never become redundant. Many of these tags have been superseded by other registrations: their record contains a Preferred-Value field that really ought to be used to form language tags representing that value.
Implementations sometimes need to describe their capabilities with regard to the rules and practices described in this document. Tags can be checked or verified in a number of ways, but two particular classes of tag conformance are formally defined here.
A tag is considered "well-formed" if it conforms to the ABNF (Syntax). Note that irregular grandfathered tags are now listed in the 'irregular' production.
A tag is considered "valid" if it satisfies these conditions:
Note that a tag's validity depends on the date of the registry used to validate the tag. A more recent copy of the registry might contain a subtag that an older version does not.
A tag is considered "valid" for a given extension (Extensions and the Extensions Registry) (as of a particular version, revision, and date) if it meets the criteria for "valid" above and also satisfies this condition:
Each subtag used in the extension part of the tag is valid according to the extension.
Some older implementations consider a tag "well-formed" if it matches the ABNF in [RFC4646] (Phillips, A. and M. Davis, "Tags for Identifying Languages," September 2006.). In that version, a well-formed tag could contain a sequence matching the obsolete 'extlang' production. Other than a few grandfathered tags (which are handled separately), no valid tags have ever matched that pattern. The difference between that ABNF and Figure 1 (Language Tag ABNF) is that the language production is replaced as follows:
obs-primary-language = (2*3ALPHA [ extlang ]) ; shortest ISO 639 code / 4ALPHA ; reserved for future use / 5*8ALPHA ; registered language subtag extlang = *3("-" 3ALPHA) ; removed in this version
| Figure 2: Obsolete Language ABNF
Older language tag implementations sometimes reference [RFC3066] (Alvestrand, H., "Tags for the Identification of Languages," January 2001.). Again, all valid tags under that version also match this document's language tag ABNF. However, a wider array of tags could be considered "well-formed" under that document. The 'Language-Tag' production used in that document matches the following:
obs-language-tag = primary-subtag *( "-" subtag ) primary-subtag = 1*8ALPHA subtag = 1*8(ALPHA / DIGIT)
| Figure 3: RFC 3066 Language Tag Syntax
Language tags may be well-formed in terms of syntax but not valid in terms of content. Users MUST NOT assign and use their own subtags, other than private-use sequences (such as "en-x-personal") or by using subtags designated as private-use in the registry (such as "no-QQ", where 'QQ' is one of a range of private-use ISO 3166-1 codes). Not only is such assignment nonconformant, it also risks collision with a future possible assignment. The private use subtags and sequences are designed for this case.
This section defines the Language Subtag Registry and the maintenance and update procedures associated with it, as well as a registry for extensions to language tags (Section 3.7 (Extensions and the Extensions Registry)).
The Language Subtag Registry contains a comprehensive list of all of the subtags valid in language tags. This allows implementers a straightforward and reliable way to validate language tags. The Language Subtag Registry will be maintained so that, except for extension subtags, it is possible to validate all of the subtags that appear in a language tag under the provisions of this document or its revisions or successors. In addition, the meaning of the various subtags will be unambiguous and stable over time. (The meaning of private use subtags, of course, is not defined by the IANA registry.)
The IANA Language Subtag Registry ("the registry") is a machine-readable file in the format described in this section, plus copies of the registration forms approved in accordance with the process described in Section 3.5 (Registration Procedure for Subtags).
Note: The existing registration forms for grandfathered and redundant tags taken from RFC 3066 have been maintained as part of the obsolete RFC 3066 registry. The subtags added to the registry by either [RFC4645] (Ewell, D., "Initial Language Subtag Registry," September 2006.) or [registry‑update] (Ewell, D., Ed., "Update to the Language Subtag Registry," September 2006.) do not have separate registration forms (so no forms are archived for these additions).
The registry consists of a series of records stored in the record-jar format (described in [record‑jar] (Raymond, E., "The Art of Unix Programming," 2003.)). Each record, in turn, consists of a series of fields that describe the various subtags and tags. The registry is a Unicode (Unicode Consortium, "The Unicode Consortium. The Unicode Standard, Version 5.0, (Boston, MA, Addison-Wesley, 2003. ISBN 0-321-49081-0)," January 2007.) [Unicode] text file, using the UTF-8 (Yergeau, F., "UTF-8, a transformation format of ISO 10646," November 2003.) [RFC3629] character encoding.
Each field can be considered a single, logical line of Unicode (Unicode Consortium, "The Unicode Consortium. The Unicode Standard, Version 5.0, (Boston, MA, Addison-Wesley, 2003. ISBN 0-321-49081-0)," January 2007.) [Unicode] characters, comprising a field-name and a field-body separated by a COLON character (%x3A). Each field is terminated by the newline sequence CRLF. The text in each field MUST be in Unicode Normalization Form C (NFC).
A collection of fields forms a 'record'. Records are separated by lines containing only the sequence "%%" (%x25.25).
Although fields are logically a single line of text, each line of text in the file format is limited to 72 bytes in length. To accommodate this, the field-body can be split into a multiple-line representation; this is called "folding". Folding is done according to customary conventions for line-wrapping. This is typically on whitespace boundaries, but can occur between other characters when the value does not include spaces, such as when a language does not use whitespace between words. In any event, there MUST NOT be breaks inside a multibyte UTF-8 sequence nor in the middle of a combining character sequence. For more information, see [UAX14] (Freitag, A., "Unicode Standard Annex #14: Line Breaking Properties," August 2006.).
Although the file format uses the UTF-8 encoding, unless otherwise indicated, fields are restricted to the printable characters from the US-ASCII (International Organization for Standardization, "ISO/IEC 646:1991, Information technology -- ISO 7-bit coded character set for information interchange.," 1991.) [ISO646] repertoire.
The format of the registry is described by the following ABNF (per [RFC5234] (Crocker, D. and P. Overell, "Augmented BNF for Syntax Specifications: ABNF," January 2008.)):
registry = record *("%%" CRLF record) record = 1*( field-name *SP ":" *SP field-body CRLF ) field-name = (ALPHA / DIGIT) [*(ALPHA / DIGIT / "-") (ALPHA / DIGIT)] field-body = *([[*SP CRLF] 1*SP] 1*CHARS) CHARS = (%x21-10FFFF) ; Unicode code points
| Figure 4: Registry Format ABNF
The sequence '..' (%x2E.2E) in a field-body denotes a range of values. Such a range represents all subtags of the same length that are in alphabetic or numeric order within that range, including the values explicitly mentioned. For example 'a..c' denotes the values 'a', 'b', and 'c' and '11..13' denotes the values '11', '12', and '13'.
All fields whose field-body contains a date value use the "full-date" format specified in [RFC3339] (Klyne, G., Ed. and C. Newman, "Date and Time on the Internet: Timestamps," July 2002.). For example: "2004-06-28" represents June 28, 2004, in the Gregorian calendar.
There are three types of records in the registry: "File-Date", "Subtag", and "Tag" records.
The first record in the registry is a "File-Date" record. This record contains the single field whose field-name is "File-Date" (see Figure 4 (Registry Format ABNF)). The field-body of this record contains the last modification date of this copy of the registry, making it possible to compare different versions of the registry. The registry on the IANA website is the most current. Versions with an older date than that one are not up-to-date.
File-Date: 2004-06-28 %%
| Figure 5: Example of the File-Date Record
Subsequent records represent either subtags or tags in the registry. "Subtag" records contain a field with a field-name of "Subtag", while, unsurprisingly, "Tag" records contain a field with a field-name of "Tag". Each of the fields in each record MUST occur no more than once, unless otherwise noted below. Each record MUST contain the following fields:
Each record MAY also contain the following fields:
Future versions of this document might add additional fields to the registry, so implementations SHOULD ignore fields found in the registry that are not defined in this document.
The 'Subtag' field MUST NOT use uppercase letters to form the subtag, with two exceptions. Subtags whose 'Type' field is 'script' (in other words, subtags defined by ISO 15924) MUST use titlecase. Subtags whose 'Type' field is 'region' (in other words, the non-numeric region subtags defined by ISO 3166-1) MUST use all uppercase. These exceptions mirror the use of case in the underlying standards.
Each subtag in the tags contained in a 'Tag' field MUST be formatted using the rules in the preceding paragraph. That is, all subtags are lowercase except for subtags that represent script or region codes.
The field 'Description' contains a description of the tag or subtag in the record. The 'Description' field MAY appear more than once per record, that is, there can be multiple descriptions for a given record. The 'Description' field MAY include the full range of Unicode characters. At least one of the 'Description' fields MUST be written or transcribed into the Latin script; additional 'Description' fields MAY also include a description in a non-Latin script. Each 'Description' field MUST be unique, both within the record in which it appears and for the collection of records of the same type. Moreover, formatting variations of the same description MUST NOT occur in that specific record or in any other record of the same type. For example, while the ISO 639-1 code 'fy' contains both the descriptions "Western Frisian" and "Frisian, Western", only one of these descriptions appears in the registry.
The 'Description' field is used for identification purposes. It doesn't necessarily represent the actual native name of the item in the record, nor are any of the descriptions guaranteed to be in any particular language (such as English or French, for example).
For subtags taken from a source standard (such as ISO 639 or ISO 15924), the 'Description' value(s) SHOULD also be taken from the source standard. Multiple descriptions in the source standard MUST be split into separate 'Description' fields. The source standard's descriptions MAY be edited, either prior to insertion or via the registration process. For fields of type 'language', the first 'Description' field appearing in the Registry corresponds to the Reference Name assigned by ISO 639-3. This helps facilitate cross-referencing between ISO 639 and the registry.
When creating or updating a record due to the action of one of the source standards, the Language Subtag Reviewer SHOULD remove duplicate or redundant descriptions and MAY edit descriptions to correct irregularities in formatting (such as misspellings, inappropriate apostrophes or other punctuation, or excessive or missing spaces) prior to submitting the proposed record to the ietf-languages list.
Note: Descriptions in registry entries that correspond to ISO 639, ISO 15924, ISO 3166-1, or UN M.49 codes are intended only to indicate the meaning of that identifier as defined in the source standard at the time it was added to the registry. The description does not replace the content of the source standard itself. The descriptions are not intended to be the localized English names for the subtags. Localization or translation of language tag and subtag descriptions is out of scope of this document.
Descriptions SHOULD contain all and only that information necessary to distinguish one subtag from others that it might be confused with. They are not intended to provide general background information, nor to provide all possible alternate names or designations.
The field 'Deprecated' MAY be added, changed, or removed from any record via the maintenance process described in Section 3.3 (Maintenance of the Registry) or via the registration process described in Section 3.5 (Registration Procedure for Subtags). Usually, the addition of a 'Deprecated' field is due to the action of one of the standards bodies, such as ISO 3166, withdrawing a code. In some historical cases, it might not have been possible to reconstruct the original deprecation date. For these cases, an approximate date appears in the registry. Although valid in language tags, subtags and tags with a 'Deprecated' field are deprecated and validating processors SHOULD NOT generate these subtags. Note that a record that contains a 'Deprecated' field and no corresponding 'Preferred-Value' field has no replacement mapping.
The field 'Preferred-Value' contains a mapping between the record in which it appears and another tag or subtag. The value in this field is strongly RECOMMENDED as the best choice to represent the value of this record when selecting a language tag. These values form three groups:
Records that contain a 'Preferred-Value' field MUST also have a 'Deprecated' field. This field contains the date on which the tag or subtag was deprecated in favor of the preferred value.
Note that 'Preferred-Value' mappings in records of type 'region' sometimes do not represent exactly the same meaning as the original value. There are many reasons for a country code to be changed, and the effect this has on the formation of language tags will depend on the nature of the change in question.
The field MAY be added, changed, or removed from records according to the rules in Section 3.3 (Maintenance of the Registry). Addition, modification, or removal of a 'Preferred-Value' field in a record does not imply that content using the affected subtag needs to be retagged.
The 'Preferred-Value' field in records of type "grandfathered" and "redundant" contains whole language tags that are strongly RECOMMENDED for use in place of the record's value. In many cases, these mappings were created via deprecation of the tags during the period before [RFC4646] (Phillips, A. and M. Davis, "Tags for Identifying Languages," September 2006.) was adopted. For example, the tag "no-nyn" was deprecated in favor of the ISO 639-1-defined language code 'nn'.
Usually the addition, removal, or change of a Preferred-Value field for a subtag is done to reflect changes in one of the source standards. For example, if an ISO 3166-1 region code is deprecated in favor of another code, that SHOULD result in the addition of a Preferred-Value field.
Changes to one subtag MAY affect other subtags as well: when proposing changes to the registry, the Language Subtag Reviewer will review the registry for such effects and propose the necessary changes using the process in Section 3.5 (Registration Procedure for Subtags), although anyone MAY request such changes. For example:
Suppose that subtag 'XX' has a Preferred-Value of 'YY'. If 'YY' later changes to have a Preferred-Value of 'ZZ', then the Preferred-Value for 'XX' MUST also change to be 'ZZ'.
Suppose that a variant subtag 'dialect' represents a language not yet available in any part of ISO 639. The later addition of a corresponding language code in ISO 639 SHOULD result in the addition of a Preferred-Value for 'dialect'.
The 'Prefix' field contains an extended language range whose subtags are appropriate to use with this subtag: each of the subtags in one of the subtag's Prefix fields SHOULD appear before the variant in a valid tag. For example, the variant subtag '1996' has a 'Prefix' field of "de". This means that tags starting with the sequence "de-" are appropriate with this subtag, so "de-Latg-1996" and "de-CH-1996" are both acceptable, while the tag "fr-1996" is an inappropriate choice.
The field of type 'Prefix' MUST NOT be removed from any record. The field-body for this type of field MAY be modified, but only if the modification broadens the meaning of the subtag. That is, the field-body can be replaced only by a prefix of itself. For example, the Prefix "be-Latn" (Belarusian, Latin script) could be replaced by the Prefix "be" (Belarusian) but not by the Prefix "ru-Latn" (Russian, Latin script).
Records of type 'variant' MAY have more than one field of type 'Prefix'. Additional fields of this type MAY be added to a 'variant' record via the registration process.
The field-body of the 'Prefix' field MUST NOT conflict with any 'Prefix' already registered for a given record. Such a conflict would occur when no valid tag could be constructed that would contain the prefix, such as when two subtags each have a 'Prefix' that contains the other subtag. For example, suppose that the subtag 'avariant' has the prefix "es-bvariant". Then the subtag 'bvariant' cannot given the prefix 'avariant', for that would require a tag of the form "es-avariant-bvariant-avariant", which would not be valid.
The field 'Suppress-Script' contains a script subtag (whose record appears in the registry). The field 'Suppress-Script' MUST only appear in records whose 'Type' field-body is 'language'. This field MUST NOT appear more than one time in a record. This field indicates a script used to write the overwhelming majority of documents for the given language. This script code therefore adds no distinguishing information to a language tag. This helps ensure greater compatibility between the language tags generated according to the rules in this document and language tags and tag processors or consumers based on RFC 3066 by indicating that the script subtag SHOULD NOT be used for most documents in that language. For example, virtually all Icelandic documents are written in the Latin script, making the subtag 'Latn' redundant in the tag "is-Latn".
Many language subtag records do not have a Suppress-Script field. The lack of a Suppress-Script might indicate that the language is customarily written in more than one script or that the language is not customarily written at all. It might also mean that sufficient information was not available when the record was created and thus remains a candidate for future registration.
The Macrolanguage field contains a primary language subtag that encompasses this subtag's language. That is, the language subtag whose record this field appears in is sometimes considered to be a sub-language of the Macrolanguage. Macrolanguage values are defined by ISO 639-3 and the exact nature of the relationship between the encompassed and encompassing languages varies on a case-by-case basis.
This field can be useful to applications or users when selecting language tags or as additional metadata useful in matching. The Macrolanguage field can only occur in records of type 'language'. Only values assigned by ISO 639-3 will be considered for inclusion. Macrolanguage fields MAY be added or removed via the normal registration process whenever ISO 639-3 defines new values or withdraws old values. Macrolanguages are informational, and MAY be removed or changed if ISO 639-3 changes the values.
For example, the language subtags 'nb' (Norwegian Bokmal) and 'nn' (Norwegian Nynorsk) each have a Macrolanguage entry of 'no' (Norwegian). For more information see Section 4.1 (Choice of Language Tag).
The field 'Comments' conveys additional information about the record and MAY appear more than once per record. The field-body MAY include the full range of Unicode characters and is not restricted to any particular script. This field MAY be inserted or changed via the registration process and no guarantee of stability is provided.
The content of this field is not restricted, except by the need to register the information, the suitability of the request, and by reasonable practical size limitations. The primary reason for the Comments field is subtag identification: to help distinguish the subtag from others with which it might be confused. In particular, large amounts of information about the use, history, or general background of a subtag are frowned upon as these generally belong and are encouraged in registration request forms themselves, but do not belong in the registry record proper.
The Language Subtag Reviewer moderates the ietf-languages mailing list, responds to requests for registration, and performs the other registry maintenance duties described in Section 3.3 (Maintenance of the Registry). Only the Language Subtag Reviewer is permitted to request IANA to change, update, or add records to the Language Subtag Registry. The Language Subtag Reviewer MAY delegate list moderation and other clerical duties as needed.
The Language Subtag Reviewer is appointed by the IESG for an indefinite term, subject to removal or replacement at the IESG's discretion. The IESG will solicit nominees for the position (upon adoption of this document or upon a vacancy) and then solicit feedback on the nominees' qualifications. Qualified candidates should be familiar with BCP 47 and its requirements; be willing to fairly, responsively, and judiciously administer the registration process; and be suitably informed about the issues of language identification so that the reviewer can assess the claims and draw upon the contributions of language experts and subtag requesters.
The subsequent performance or decisions of the Language Subtag Reviewer MAY be appealed to the IESG under the same rules as other IETF decisions (see [RFC2026] (Bradner, S., "The Internet Standards Process -- Revision 3," October 1996.)). The IESG can reverse or overturn the decisions of the Language Subtag Reviewer, provide guidance, or take other appropriate actions.
Maintenance of the registry requires that as codes are assigned or withdrawn by ISO 639, ISO 15924, ISO 3166, and UN M.49, the Language Subtag Reviewer MUST evaluate each change and determine the appropriate course of action according to the rules in this document. Such updates follow the registration process described in Section 3.5 (Registration Procedure for Subtags). Usually the Language Subtag Reviewer will start the process for the new or updated record by filling in the registration form and submitting it. If a change to one of these standards takes place and the Language Subtag Reviewer does not do this in a timely manner, then any interested party MAY submit the form. Thereafter the registration process continues normally.
Note that some registrations affect other subtags--perhaps more than one--as when a region subtag is being deprecated in favor of a new value. The Language Subtag Reviewer is responsible for ensuring that any such changes are properly registered, with each change requiring its own registration form.
The Language Subtag Reviewer MUST ensure that new subtags meet the requirements elsewhere in this document (and most especially in Section 3.4 (Stability of IANA Registry Entries)) or submit an appropriate registration form for an alternate subtag as described in that section. Each individual subtag affected by a change MUST be sent to the ietf-languages list with its own registration form and in a separate message.
The stability of entries and their meaning in the registry is critical to the long-term stability of language tags. The rules in this section guarantee that a specific language tag's meaning is stable over time and will not change.
These rules specifically deal with how changes to codes (including withdrawal and deprecation of codes) maintained by ISO 639, ISO 15924, ISO 3166, and UN M.49 are reflected in the IANA Language Subtag Registry. Assignments to the IANA Language Subtag Registry MUST follow the following stability rules:
- Example
- The region code 'TL' was assigned to the country 'Timor-Leste', replacing the code 'TP' (which was assigned to 'East Timor' when it was under administration by Portugal). The subtag 'TP' remains valid in language tags, but its record contains the a 'Preferred-Value' of 'TL' and its field 'Deprecated' contains the date the new code was assigned ('2004-07-06').
- For ISO 639 codes, if the newly assigned code's meaning is not represented by a subtag in the IANA registry, the Language Subtag Reviewer, as described in Section 3.5 (Registration Procedure for Subtags), SHALL prepare a proposal for entering in the IANA registry as soon as practical a registered language subtag as an alternate value for the new code. The form of the registered language subtag will be at the discretion of the Language Subtag Reviewer and MUST conform to other restrictions on language subtags in this document.
- For all subtags whose meaning is derived from an external standard (that is, by ISO 639, ISO 15924, ISO 3166-1, or UN M.49), if a new meaning is assigned to an existing code and the new meaning broadens the meaning of that code, then the meaning for the associated subtag MAY be changed to match. The meaning of a subtag MUST NOT be narrowed, however, as this can result in an unknown proportion of the existing uses of a subtag becoming invalid. Note: ISO 639 maintenance agency/registration authority (MA/RA) has adopted a similar stability policy.
- For ISO 15924 codes, if the newly assigned code's meaning is not represented by a subtag in the IANA registry, the Language Subtag Reviewer, as described in Section 3.5 (Registration Procedure for Subtags), SHALL prepare a proposal for entering in the IANA registry as soon as practical a registered variant subtag as an alternate value for the new code. The form of the registered variant subtag will be at the discretion of the Language Subtag Reviewer and MUST conform to other restrictions on variant subtags in this document.
- For ISO 3166-1 codes, if the newly assigned code's meaning is associated with the same UN M.49 code as another 'region' subtag, then the existing region subtag remains as the preferred value for that region and no new entry is created. A comment MAY be added to the existing region subtag indicating the relationship to the new ISO 3166-1 code.
- For ISO 3166-1 codes, if the newly assigned code's meaning is associated with a UN M.49 code that is not represented by an existing region subtag, then the Language Subtag Reviewer, as described in Section 3.5 (Registration Procedure for Subtags), SHALL prepare a proposal for entering the appropriate UN M.49 country code as an entry in the IANA registry.
- For ISO 3166-1 codes, if there is no associated UN numeric code, then the Language Subtag Reviewer SHALL petition the UN to create one. If there is no response from the UN within ninety days of the request being sent, the Language Subtag Reviewer SHALL prepare a proposal for entering in the IANA registry as soon as practical a registered variant subtag as an alternate value for the new code. The form of the registered variant subtag will be at the discretion of the Language Subtag Reviewer and MUST conform to other restrictions on variant subtags in this document. This situation is very unlikely to ever occur.
Note: The redundant and grandfathered entries together are the complete list of tags registered under [RFC3066] (Alvestrand, H., "Tags for the Identification of Languages," January 2001.). The redundant tags are those that can now be formed using the subtags defined in the registry together with the rules of Section 2.2 (Language Subtag Sources and Interpretation). The grandfathered entries include those that can never be legal under those same provisions plus those tags that contain subtags not yet registered or, perhaps, inappropriate for registration.
The set of redundant and grandfathered tags is permanent and stable: new entries in this section MUST NOT be added and existing entries MUST NOT be removed. Records of type 'grandfathered' MAY have their type converted to 'redundant'; see item 12 in Section 3.6 (Possibilities for Registration) for more information. The decision-making process about which tags were initially grandfathered and which were made redundant is described in [RFC4645] (Ewell, D., "Initial Language Subtag Registry," September 2006.).
RFC 3066 tags that were deprecated prior to the adoption of [RFC4646] (Phillips, A. and M. Davis, "Tags for Identifying Languages," September 2006.) are part of the list of grandfathered tags, and their component subtags were not included as registered variants (although they remain eligible for registration). For example, the tag "art-lojban" was deprecated in favor of the language subtag 'jbo'.
The procedure given here MUST be used by anyone who wants to use a subtag not currently in the IANA Language Subtag Registry.
Only subtags of type 'language' and 'variant' will be considered for independent registration of new subtags. Subtags needed for stability and subtags necessary to keep the registry synchronized with ISO 639, ISO 15924, ISO 3166, and UN M.49 within the limits defined by this document also use this process, as described in Section 3.3 (Maintenance of the Registry). Stability provisions are described in Section 3.4 (Stability of IANA Registry Entries).
This procedure MAY also be used to register or alter the information for the 'Comments', 'Deprecated', 'Description', 'Prefix', 'Preferred-Value', or 'Suppress-Script' fields in a subtag's record as described in Section 3.4 (Stability of IANA Registry Entries). Changes to all other fields in the IANA registry are NOT permitted.
Registering a new subtag or requesting modifications to an existing tag or subtag starts with the requester filling out
the registration form reproduced below. Note that each response is not limited
in size so that the request can adequately describe the registration.
The fields in the "Record Requested" section SHOULD follow the requirements in Section 3.1 (Format of the IANA Language Subtag Registry).
LANGUAGE SUBTAG REGISTRATION FORM 1. Name of requester: 2. E-mail address of requester: 3. Record Requested: Type: Subtag: Description: Prefix: Preferred-Value: Deprecated: Suppress-Script: Macrolanguage: Comments: 4. Intended meaning of the subtag: 5. Reference to published description of the language (book or article): 6. Any other relevant information:
| Figure 6: The Language Subtag Registration Form
Examples of completed registration forms can be found in Appendix C (Examples of Registration Forms) or online at http://www.iana.org/assignments/lang-subtags-templates/.
The subtag registration form MUST be sent to <email@example.com> for a two-week review period before it can be submitted to IANA. If modifications are made to the request during the course of the registration process (such as corrections to meet the requirements in Section 3.1 (Format of the IANA Language Subtag Registry)) the modified form MUST also be sent to <email@example.com> at least one week prior to submission to IANA.
The ietf-languages list is an open list and can be joined by sending a request to <email@example.com>. The list can be hosted by IANA or by any third party at the request of IESG.
Before forwarding a new registration to IANA, the Language Subtag Reviewer MUST ensure that all requirements in this document are met and that values in the 'Subtag' field match case according to the description in Section 3.1 (Format of the IANA Language Subtag Registry). The Reviewer MUST also ensure that an appropriate File-Date record is included in the request, to assist IANA when updating the registry (see Section 5.1 (Language Subtag Registry)).
Some fields in both the registration form as well as the registry record itself permit the use of non-ASCII characters. Registration requests SHOULD use the UTF-8 encoding for consistency and clarity. However, since some mail clients do not support this encoding, other encodings MAY be used for the registration request. The Language Subtag Reviewer is responsible for ensuring that the proper Unicode characters appear in both the archived request form and the registry record. In the case of a transcription or encoding error by IANA, the Language Subtag Reviewer will request that the registry be repaired, providing any necessary information to assist IANA.
Variant subtags are usually registered for use with a particular range of language tags. For example, the subtag 'rozaj' is intended for use with language tags that start with the primary language subtag "sl", since Resian is a dialect of Slovenian. Thus, the subtag 'rozaj' would be appropriate in tags such as "sl-Latn-rozaj" or "sl-IT-rozaj". This information is stored in the 'Prefix' field in the registry. Variant registration requests SHOULD include at least one 'Prefix' field in the registration form.
The 'Prefix' field for a given registered subtag exists in the IANA registry as a guide to usage. Additional prefixes MAY be added by filing an additional registration form. In that form, the "Any other relevant information:" field MUST indicate that it is the addition of a prefix.
Requests to add a prefix to a variant subtag that imply a different semantic meaning SHOULD be rejected. For example, a request to add the prefix "de" to the subtag 'nedis' so that the tag "de-nedis" represented some German dialect would be rejected. The 'nedis' subtag represents a particular Slovenian dialect and the additional registration would change the semantic meaning assigned to the subtag. A separate subtag SHOULD be proposed instead.
The 'Description' field MUST contain a description of the tag being registered written or transcribed into the Latin script; it MAY also include a description in a non-Latin script. The 'Description' field is used for identification purposes and doesn't necessarily represent the actual native name of the language or variation or to be in any particular language.
While the 'Description' field itself is not guaranteed to be stable and errata corrections MAY be undertaken from time to time, attempts to provide translations or transcriptions of entries in the registry itself will probably be frowned upon by the community or rejected outright, as changes of this nature have an impact on the provisions in Section 3.4 (Stability of IANA Registry Entries).
When the two-week period has passed, the Language Subtag Reviewer MUST take one of the following actions:
Note that the Language Subtag Reviewer MAY raise objections on the list if he or she so desires. The important thing is that the objection MUST be made publicly.
Sometimes the request needs to be modified as a result of discussion during the review period or due to requirements in this document. The applicant, Language Subtag Reviewer, or others are free to submit a modified version of the completed registration form, which will be considered in lieu of the original request with the explicit approval of the applicant. Such changes do not restart the two-week discussion period, although an application containing the final record submitted to IANA MUST appear on the list at least one week prior to the Language Subtag Reviewer forwarding the record to IANA. The applicant is also free to modify a rejected application with additional information and submit it again; this starts a new two-week comment period.
Registrations initiated due to the provisions of Section 3.3 (Maintenance of the Registry) or Section 3.4 (Stability of IANA Registry Entries) SHALL NOT be rejected altogether (since they have to ultimately appear in the registry) and SHOULD be completed as quickly as possible. The review process allows list members to comment on the specific information in the form and the record it contains and thus help ensure that it is correct and consistent. The Language Subtag Reviewer MAY reject a specific version of the form, but MUST include in the rejection a suitable replacement, extending the review period as described above, until the form is in a format worthy of reviewer's approval.
Decisions made by the Language Subtag Reviewer MAY be appealed to the IESG [RFC2028] (Hovey, R. and S. Bradner, "The Organizations Involved in the IETF Standards Process," October 1996.) under the same rules as other IETF decisions [RFC2026] (Bradner, S., "The Internet Standards Process -- Revision 3," October 1996.). This includes a decision to extend the review period or the failure to announce a decision in a clear and timely manner.
The approved records appear in the Language Subtag Registry. The approved registration forms are available online under http://www.iana.org/assignments/lang-subtags-templates/.
Updates or changes to existing records follow the same procedure as new registrations. The Language Subtag Reviewer decides whether there is consensus to update the registration following the two week review period; normally, objections by the original registrant will carry extra weight in forming such a consensus.
Registrations are permanent and stable. Once registered, subtags will not be removed from the registry and will remain a valid way in which to specify a specific language or variant.
Note: The purpose of the "Reference to published description" section in the registration form is to aid in verifying whether a language is registered or what language or language variation a particular subtag refers to. In most cases, reference to an authoritative grammar or dictionary of that language will be useful; in cases where no such work exists, other well-known works describing that language or in that language MAY be appropriate. The Language Subtag Reviewer decides what constitutes "good enough" reference material. This requirement is not intended to exclude particular languages or dialects due to the size of the speaker population or lack of a standardized orthography. Minority languages will be considered equally on their own merits.
Possibilities for registration of subtags or information about subtags include:
Subtags proposed for registration that would cause all or part of a grandfathered tag to become redundant but whose meaning conflicts with or alters the meaning of the grandfathered tag MUST be rejected.
This document leaves the decision on what subtags or changes to subtags are appropriate (or not) to the registration process described in Section 3.5 (Registration Procedure for Subtags).
Note: four-character primary language subtags are reserved to allow for the possibility of alpha4 codes in some future addition to the ISO 639 family of standards.
ISO 639 defines a maintenance agency for additions to and changes in the list of languages in ISO 639. This agency is:
International Information Centre for Terminology (Infoterm)
Aichholzgasse 6/12, AT-1120
Wien, Austria
Phone: +43 1 26 75 35 Ext. 312 Fax: +43 1 216 32 72
ISO 639-2 defines a maintenance agency for additions to and changes in the list of languages in ISO 639-2. This agency is:
Library of Congress
Network Development and MARC Standards Office
Washington, D.C. 20540 USA
Phone: +1 202 707 6237 Fax: +1 202 707 0115
URL: http://www.loc.gov/standards/iso639-2
ISO 639-3 defines a maintenance agency for additions to and changes in the list of languages in ISO 639-3. This agency is:
SIL International
ISO 639-3 Registrar
7500 W. Camp Wisdom Rd.
Dallas, TX 75236 USA
Phone: +1 972 708 7400, ext. 2293 Fax: +1 972 708 7546
Email: email@example.com
URL: http://www.sil.org/iso639-3
The maintenance agency for ISO 3166-1 (country codes) is:
ISO 3166 Maintenance Agency
c/o International Organization for Standardization
Case postale 56
CH-1211 Geneva 20 Switzerland
Phone: +41 22 749 72 33 Fax: +41 22 749 73 49
URL: http://www.iso.org/iso/en/prods-services/iso3166ma/index.html
The registration authority for ISO 15924 (script codes) is:
Unicode Consortium Box 391476
Mountain View, CA 94039-1476, USA
URL: http://www.unicode.org/iso15924
The Statistics Division of the United Nations Secretariat maintains the Standard Country or Area Codes for Statistical Use and can be reached at:
Statistical Services Branch
Statistics Division
United Nations, Room DC2-1620
New York, NY 10017, USA
Fax: +1-212-963-0623
E-mail: email@example.com
URL: http://unstats.un.org/unsd/methods/m49/m49alpha.htm
Extension subtags are those introduced by single-character subtags ("singletons") other than 'x'. They are reserved for the generation of identifiers that contain a language component and are compatible with applications that understand language tags.
The structure and form of extensions are defined by this document so that implementations can be created that are forward compatible with applications that might be created using singletons in the future. In addition, defining a mechanism for maintaining singletons will lend stability to this document by reducing the likely need for future revisions or updates.
Single-character subtags are assigned by IANA using the "IETF Consensus" policy defined by [RFC2434] (Narten, T. and H. Alvestrand, "Guidelines for Writing an IANA Considerations Section in RFCs," October 1998.). This policy requires the development of an RFC, which SHALL define the name, purpose, processes, and procedures for maintaining the subtags. The maintaining or registering authority, including name, contact email, discussion list email, and URL location of the registry, MUST be indicated clearly in the RFC. The RFC MUST specify or include each of the following:
IANA will maintain a registry of allocated single-character (singleton) subtags. This registry MUST use the record-jar format described by the ABNF in Section 3.1 (Format of the IANA Language Subtag Registry). Upon publication of an extension as an RFC, the maintaining authority defined in the RFC MUST forward this registration form to email@example.com, who MUST forward the request to email@example.com. The maintaining authority of the extension MUST maintain the accuracy of the record by sending an updated full copy of the record to email@example.com with the subject line "LANGUAGE TAG EXTENSION UPDATE" whenever content changes. Only the 'Comments', 'Contact_Email', 'Mailing_List', and 'URL' fields MAY be modified in these updates.
Failure to maintain this record, maintain the corresponding registry, or meet other conditions imposed by this section of this document MAY be appealed to the IESG [RFC2028] (Hovey, R. and S. Bradner, "The Organizations Involved in the IETF Standards Process," October 1996.) under the same rules as other IETF decisions (see [RFC2026] (Bradner, S., "The Internet Standards Process -- Revision 3," October 1996.)) and MAY result in the authority to maintain the extension being withdrawn or reassigned by the IESG.
%% Identifier: Description: Comments: Added: RFC: Authority: Contact_Email: Mailing_List: URL: %%
| Figure 7: Format of Records in the Language Tag Extensions Registry
'Identifier' contains the single-character subtag (singleton) assigned to the extension. The Internet-Draft submitted to define the extension SHOULD specify which letter or digit to use, although the IESG MAY change the assignment when approving the RFC.
'Description' contains the name and description of the extension.
'Comments' is an OPTIONAL field and MAY contain a broader description of the extension.
'Added' contains the date the extension's RFC was published in the "full-date" format specified in [RFC3339] (Klyne, G., Ed. and C. Newman, "Date and Time on the Internet: Timestamps," July 2002.). For example: 2004-06-28 represents June 28, 2004, in the Gregorian calendar.
'RFC' contains the RFC number assigned to the extension.
'Authority' contains the name of the maintaining authority for the extension.
'Contact_Email' contains the email address used to contact the maintaining authority.
'Mailing_List' contains the URL or subscription email address of the mailing list used by the maintaining authority.
'URL' contains the URL of the registry for this extension.
The determination of whether an Internet-Draft meets the above conditions and the decision to grant or withhold such authority rests solely with the IESG and is subject to the normal review and appeals process associated with the RFC process.
Extension authors are strongly cautioned that many (including most well-formed) processors will be unaware of any special relationships or meaning inherent in the order of extension subtags. Extension authors SHOULD avoid subtag relationships or canonicalization mechanisms that interfere with matching or with length restrictions that sometimes exist in common protocols where the extension is used. In particular, applications MAY truncate the subtags in doing matching or in fitting into limited lengths, so it is RECOMMENDED that the most significant information be in the most significant (left-most) subtags and that the specification gracefully handle truncated subtags.
When a language tag is to be used in a specific, known, protocol, it is RECOMMENDED that the language tag not contain extensions not supported by that protocol. In addition, note that some protocols MAY impose upper limits on the length of the strings used to store or transport the language tag.
Upon adoption of this document the IANA Language Subtag Registry will need an update so that it contains the complete set of subtags valid in a language tag. This collection of subtags, along with a description of the process used to create it, is described by [registry‑update] (Ewell, D., Ed., "Update to the Language Subtag Registry," September 2006.). IANA will publish the updated version of the registry described by this document using the instructions and content of [registry‑update] (Ewell, D., Ed., "Update to the Language Subtag Registry," September 2006.). Once published by IANA, the maintenance procedures, rules, and registration processes described in this document will be available for new registrations or updates.
Registrations that are in process under the rules defined in [RFC4646] (Phillips, A. and M. Davis, "Tags for Identifying Languages," September 2006.) when this document is adopted MUST be completed under the rules contained in this document.
This section addresses how to use the information in the registry with the tag syntax to choose, form, and process language tags.
The guiding principle in forming language tags is to "tag content wisely." Sometimes there is a choice between several possible tags for the same content. The choice of which tag to use depends on the content and application in question and some amount of judgment might be necessary when selecting a tag.
Interoperability is best served when the same language tag is used consistently to represent the same language. If an application has requirements that make the rules here inapplicable, then that application risks damaging interoperability. It is strongly RECOMMENDED that users not define their own rules for language tag choice.
A subtag SHOULD only be used when it adds useful distinguishing information to the tag. Extraneous subtags interfere with the meaning, understanding, and processing of language tags. In particular, users and implementations SHOULD follow the 'Prefix' and 'Suppress-Script' fields in the registry (defined in Section 3.1 (Format of the IANA Language Subtag Registry)): these fields provide guidance on when specific additional subtags SHOULD be used or avoided in a language tag.
Some applications can benefit from the use of script subtags in language tags, as long as the use is consistent for a given context. Script subtags are never appropriate for unwritten content (such as audio recordings).
Script subtags were formally defined in BCP 47 by [RFC4646] (Phillips, A. and M. Davis, "Tags for Identifying Languages," September 2006.). Their use can affect matching and subtag identification for implementations of previous versions of BCP 47 (i.e. [RFC1766] (Alvestrand, H., "Tags for the Identification of Languages," March 1995.) or [RFC3066] (Alvestrand, H., "Tags for the Identification of Languages," January 2001.)), as these subtags appear between the primary language and region subtags. For example, if an implementation selects content using Basic Filtering (Phillips, A. and M. Davis, "Matching of Language Tags," September 2006.) [RFC4647] (originally described in Section 2.5 of [RFC3066] (Alvestrand, H., "Tags for the Identification of Languages," January 2001.)) and the user requested the language range "en-US", content labeled "en-Latn-US" will not match the request and thus not be selected. Therefore, it is important to know when script subtags will customarily be used and when they ought not be used. In the registry, the Suppress-Script field helps ensure greater compatibility between the language tags by defining when users SHOULD NOT include a script subtag with a particular primary language subtag.
The choice of subtags used to form a language tag SHOULD follow these guidelines:
Some of the languages in the registry are labeled "macrolanguages" by ISO 639-3, which defines the term as "clusters of closely-related language varieties that [...] can be considered distinct individual languages, yet in certain usage contexts a single language identity for all is needed". These correspond to codes registered in ISO 639-2 as single languages that were found to correspond to more than one language in ISO 639-3. The record for each of the languages encompassed by a macrolanguage contains a 'Macrolanguage' field in the registry; the macrolanguages themselves are not specially marked.
It is always permitted, and sometimes useful, to tag an encompassed language using the subtag for its macrolanguage. However, the Macrolanguage field doesn't define what the relationship is between the encompassed language and its macrolanguage, nor does it define how languages encompassed by the same macrolanguage are related to each other. In some cases, one of the encompassed languages serves as a standard form for the entire macrolanguage and is frequently identified with it; in other cases there is no dominant language, and the macrolanguage simply serves as a cover term for the entire group.
Applications MAY use macrolanguage information to improve matching or language negotiation. For example, the information that 'sr' (Serbian) and 'hr' (Croatian) share a macrolanguage expresses a closer relation between those languages than between, say, 'sr' (Serbian) and 'ma' (Macedonian). It is valid to use either the subtag of the encompassed language or of the macrolanguage to form language tags. However, many matching applications will not be aware of the relationship between the languages. Care in selecting which subtags are used is crucial to interoperability.
In general, use the most specific subtag to form the language tag. However, where the macrolanguage tag has been historically used to denote a dominant encompassed language, it SHOULD be used in place of the subtag specific to that encompassed language unless it is necessary to clearly distinguish the macrolanguage as a whole from that enclosed dominant language variety.
The pairs of macro and encompassed languages affected by this issue when this document was published were:
Arabic 'ar' Standard Arabic 'arb' Konkani (macrolanguage) 'kok' Konkani (single language) 'knn' Malay (macrolanguage) 'ms' Malay (single language) 'mly' Swahili (macrolanguage) 'sw' Swahili (single language) 'swh' Uzbek 'uz' Northern Uzbek 'uzn' Chinese 'zh' Mandarin Chinese 'cmn'
| Figure 8
In particular, the Chinese family of languages call for special consideration. Because the written form is very similar for most languages having 'zh' (Chinese) as a macrolanguage (and because historically subtags for the various encompassed languages were not available), languages such as 'yue' (Cantonese) have historically used either 'zh' or a tag (now grandfathered) beginning with 'zh'. This means that macrolanguage information can be usefully applied when searching for content or when providing fallbacks in language negotiation. For example, the information that 'yue' has a macrolangauge of 'zh' could be used in the Lookup algorithm to fallback from a request for "yue-Hans-CN" to "zh-Hans-CN" without losing the script and region information (even though the user did not specify "zh-Hans-CN" in their request).
To ensure consistent backward compatibility, this document contains several provisions to account for potential instability in the standards used to define the subtags that make up language tags. These provisions mean that no language tag created under the rules in this document will become invalid, nor will a language tag have a narrower scope in the future (it may have a broader scope).
Standards, protocols, and applications that reference this document normatively but apply different rules to the ones given in this section MUST specify how language tag selection varies from the guidelines given here.
The meaning of a language tag is related to the meaning of the subtags that it contains. Each subtag, in turn, implies a certain range of expectations one might have for related content, although it is not a guarantee. For example, the use of a script subtag such as 'Arab' (Arabic script) does not mean that the content contains only Arabic characters. It does mean that the language involved is predominantly in the Arabic script. Thus a language tag and its subtags can encompass a very wide range of variation and yet remain appropriate in each particular instance.
Validity of a tag is not the only factor determining its usefulness. While every valid tag has a meaning, it might not represent any real-world language usage. This is unavoidable in a system in which subtags can be combined freely. For example, tags such as "ar-Cyrl-CO" (Arabic, Cyrillic script, as used in Colombia ) or "tlh-Kore-AQ-fonipa" (Klingon, Korean script, as used in Antarctica, IPA phonetic transcription) are both valid and unlikely to represent a useful combination of language attributes.
The meaning of a given tag doesn't depend on the context in which it appears. The relationship between a tag's meaning and the information objects to which that tag is applied, however, can vary.
Language tags are related when they contain a similar sequence of subtags. For example, if a language tag B contains language tag A as a prefix, then B is typically "narrower" or "more specific" than A. Thus, "zh-Hant-TW" is more specific than "zh-Hant".
This relationship is not guaranteed in all cases: specifically, languages that begin with the same sequence of subtags are NOT guaranteed to be mutually intelligible, although they might be. For example, the tag "az" shares a prefix with both "az-Latn" (Azerbaijani written using the Latin script) and "az-Cyrl" (Azerbaijani written using the Cyrillic script). A person fluent in one script might not be able to read the other, even though the text might be identical. Content tagged as "az" most probably is written in just one script and thus might not be intelligible to a reader familiar with the other script.
Similarly, not all subtags specify an actual distinction in language. For example, the tags "en-US" and "en-CA" mean, roughly, English with features generally thought to be characteristic of the United States and Canada, respectively. They do not imply that a significant dialectical boundary exists between any arbitrarily selected point in the United States and any arbitrarily selected point in Canada. Neither does a particular region subtag imply that linguistic distinctions do not exist within that region.
There is no defined upper limit on the size of language tags. While historically most language tags have consisted of language and region subtags with a combined total length of up to six characters, larger tags have always been both possible and actually appeared in use.
Neither the language tag syntax nor other requirements in this document impose a fixed upper limit on the number of subtags in a language tag (and thus an upper bound on the size of a tag). The language tag syntax suggests that, depending on the specific language, more subtags (and thus a longer tag) are sometimes necessary to completely identify the language for certain applications; thus, it is possible to envision long or complex subtag sequences.
Some applications and protocols are forced to allocate fixed buffer sizes or otherwise limit the length of a language tag. A conformant implementation or specification MAY refuse to support the storage of language tags that exceed a specified length. Any such limitation SHOULD be clearly documented, and such documentation SHOULD include what happens to longer tags (for example, whether an error value is generated or the language tag is truncated). A protocol that allows tags to be truncated at an arbitrary limit, without giving any indication of what that limit is, has the potential for causing harm by changing the meaning of tags in substantial ways.
In practice, most language tags do not require more than a few subtags and will not approach reasonably sized buffer limitations; see Section 4.1 (Choice of Language Tag).
Some specifications or protocols have limits on tag length but do not have a fixed length limitation. For example, [RFC2231] (Freed, N. and K. Moore, "MIME Parameter Value and Encoded Word Extensions: Character Sets, Languages, and Continuations," November 1997.) has no explicit length limitation: the length available for the language tag is constrained by the length of other header components (such as the charset's name) coupled with the 76-character limit in [RFC2047] (Moore, K., "MIME (Multipurpose Internet Mail Extensions) Part Three: Message Header Extensions for Non-ASCII Text," November 1996.). Thus, the "limit" might be 50 or more characters, but it could potentially be quite small.
The considerations for assigning a buffer limit are:
Implementations SHOULD NOT truncate language tags unless the meaning of the tag is purposefully being changed, or unless the tag does not fit into a limited buffer size specified by a protocol for storage or transmission.
Implementations SHOULD warn the user when a tag is truncated since truncation changes the semantic meaning of the tag.
Implementations of protocols or specifications that are space constrained but do not have a fixed limit SHOULD use the longest possible tag in preference to truncation.
Protocols or specifications that specify limited buffer sizes for language tags MUST allow for language tags of up to 33 characters.
Protocols or specifications that specify limited buffer sizes for language tags SHOULD allow for language tags of at least 30 characters. Note that RFC 4646 (Phillips, A. and M. Davis, "Tags for Identifying Languages," September 2006.) [RFC4646] recommended a field size of 42 character because it included the permanently reserved (and unused) 'extlang' production. The current size recommendation does not include the use of the 'extlang' field. Protocols or specifications that commonly use extensions or private use subtags might wish to reserve or recommend a longer "minimum buffer" size.
The following illustration shows how the 30-character recommendation was derived:
language = 3 (ISO 639-2; ISO 639-1 requires 2) script = 5 (if not suppressed: see Section 4.1) region = 4 (UN M.49; ISO 3166-1 requires 3) variant1 = 9 (needs 'language' as a prefix) variant2 = 9 (needs 'language-variant1' as a prefix) total = 30 characters
| Figure 9: Derivation of the Limit on Tag Length
Truncation of a language tag alters the meaning of the tag, and thus SHOULD be avoided. However, truncation of language tags is sometimes necessary due to limited buffer sizes. Such truncation MUST NOT permit a subtag to be chopped off in the middle or the formation of invalid tags (for example, one ending with the "-" character).
This means that applications or protocols that truncate tags MUST do so by progressively removing subtags along with their preceding "-" from the right side of the language tag until the tag is short enough for the given buffer. If the resulting tag ends with a single-character subtag, that subtag and its preceding "-" MUST also be removed. For example:
Tag to truncate: zh-Latn-CN-variant1-a-extend1-x-wadegile-private1 1. zh-Latn-CN-variant1-a-extend1-x-wadegile 2. zh-Latn-CN-variant1-a-extend1 3. zh-Latn-CN-variant1 4. zh-Latn-CN 5. zh-Latn 6. zh
| Figure 10: Example of Tag Truncation
Since a particular language tag is sometimes used by many processes, language tags SHOULD always be created or generated in a canonical form.
A language tag is in canonical form when:
Example: The language tag "en-a-aaa-b-ccc-bbb-x-xyz" is in canonical form, while "en-b-ccc-bbb-a-aaa-X-xyz" is well-formed and potentially valid (extensions 'a' and 'b' are not defined as of the publication of this document) but not in canonical form (the extensions are not in alphabetical order).
Example: The language tag "en-BU" (English as used in Burma) is not canonical because the 'BU' subtag has a canonical mapping to 'MM' (Myanmar), although the tag "en-BU" maintains its validity.
Canonicalization of language tags does not imply anything about the use of upper or lowercase letters when processing or comparing subtags (and as described in Section 2.1 (Syntax)). All comparisons MUST be performed in a case-insensitive manner.
When performing canonicalization of language tags, processors MAY regularize the case of the subtags (that is, this process is OPTIONAL), following the case used in the registry. Note that this corresponds to the following casing rules: uppercase all non-initial two-letter subtags; titlecase all non-initial four-letter subtags; lowercase everything else.
Note: Case folding of ASCII letters in certain locales, unless carefully handled, sometimes produces non-ASCII character values. The Unicode Character Database file "SpecialCasing.txt" defines the specific cases that are known to cause problems with this. In particular, the letter 'i' (U+0069) in Turkish and Azerbaijani is uppercased to U+0130 (LATIN CAPITAL LETTER I WITH DOT ABOVE). Implementers SHOULD specify a locale-neutral casing operation to ensure that case folding of subtags does not produce this value, which is illegal in language tags. For example, if one were to uppercase the region subtag 'in' using Turkish locale rules, the sequence U+0130 U+004E would result instead of the expected 'IN'.
Note: if the field 'Deprecated' appears in a registry record without an accompanying 'Preferred-Value' field, then that tag or subtag is deprecated without a replacement. Validating processors SHOULD NOT generate tags that include these values, although the values are canonical when they appear in a language tag.
An extension MUST define any relationships that exist between the various subtags in the extension and thus MAY define an alternate canonicalization scheme for the extension's subtags. Extensions MAY define how the order of the extension's subtags are interpreted. For example, an extension could define that its subtags are in canonical order when the subtags are placed into ASCII order: that is, "en-a-aaa-bbb-ccc" instead of "en-a-ccc-bbb-aaa". Another extension might define that the order of the subtags influences their semantic meaning (so that "en-b-ccc-bbb-aaa" has a different value from "en-b-aaa-bbb-ccc"). However, extension specifications SHOULD be designed so that they are tolerant of the typical processes described in Section 3.7 (Extensions and the Extensions Registry).
Private use subtags, like all other subtags, MUST conform to the format and content constraints in the ABNF. Private use subtags have no meaning outside the private agreement between the parties that intend to use or exchange language tags that employ them. The same subtags MAY be used with a different meaning under a separate private agreement. They SHOULD NOT be used where alternatives exist and SHOULD NOT be used in content or protocols intended for general use.
Private use subtags are simply useless for information exchange without prior arrangement. The value and semantic meaning of private use tags and of the subtags used within such a language tag are not defined by this document.
Subtags defined in the IANA registry as having a specific private use meaning convey more information that a purely private use tag prefixed by the singleton subtag 'x'. For applications, this additional information MAY be useful.
For example, the region subtags 'AA', 'ZZ', and in the ranges 'QM'-'QZ' and 'XA'-'XZ' (derived from ISO 3166-1 private use codes) MAY be used to form a language tag. A tag such as "zh-Hans-XQ" conveys a great deal of public, interchangeable information about the language material (that it is Chinese in the simplified Chinese script and is suitable for some geographic region 'XQ'). While the precise geographic region is not known outside of private agreement, the tag conveys far more information than an opaque tag such as "x-someLang", which contains no information about the language subtag or script subtag outside of the private agreement.
However, in some cases content tagged with private use subtags MAY interact with other systems in a different and possibly unsuitable manner compared to tags that use opaque, privately defined subtags, so the choice of the best approach sometimes depends on the particular domain in question.
This section deals with the processes and requirements necessary for IANA to undertake to maintain the subtag and extension registries as defined by this document and in accordance with the requirements of [RFC2434] (Narten, T. and H. Alvestrand, "Guidelines for Writing an IANA Considerations Section in RFCs," October 1998.).
The impact on the IANA maintainers of the two registries defined by this document will be a small increase in the frequency of new entries or updates. IANA also is required to create a new mailing list (described below in Section 5.1 (Language Subtag Registry)) to announce registry changes and updates.
Upon adoption of this document, IANA will update the registry using instructions and content provided in a companion document: [registry‑update] (Ewell, D., Ed., "Update to the Language Subtag Registry," September 2006.). The criteria and process for selecting the updated set of records are described in that document. The updated set of records represents no impact on IANA, since the work to create it will be performed externally.
Future work on the Language Subtag Registry includes the following activities:
Each registration form sent to IANA contains a single record for incorporation into the registry. The form will be sent to "firstname.lastname@example.com" by the Language Subtag Reviewer. It will have a subject line indicating whether the enclosed form represents an insertion of a new record (indicated by the word "INSERT" in the subject line) or a replacement of an existing record (indicated by the word "MODIFY" in the subject line). At no time can a record be deleted from the registry.
IANA will extract the record from the form and place the inserted or modified record into the appropriate section of the language subtag registry, grouping the records by their 'Type' field. Inserted records can be placed anywhere in the appropriate section; there is no guarantee of the order of the records beyond grouping them together by 'Type'. Modified records overwrite the record they replace.
Whenever an entry is created or modified in the registry, the 'File-Date' record at the start of the registry is updated to reflect the most recent modification date in the [RFC3339] (Klyne, G., Ed. and C. Newman, "Date and Time on the Internet: Timestamps," July 2002.) "full-date" format: included in any request to insert or modify records will be a new File-Date record indicating the acceptance date of the record. This record is to be placed first in the registry, replacing the existing File-Date record. In the event that the File-Date record present in the registry has a later date than the record being inserted or modified, then the latest (most recent) record will be preserved. IANA should attempt to process multiple registration requests in order according to the File-Date in the form, since one registration could otherwise cause a more recent change to be overwritten.
The updated registry file MUST use the UTF-8 character encoding and IANA MUST check the registry file for proper encoding. Non-ASCII characters can be sent to IANA by attaching the registration form to the email message or by using various encodings in the mail message body (UTF-8 is recommended). IANA will verify any unclear or corrupted characters with the Language Subtag Reviewer prior to posting the updated registry.
IANA will also archive and make publicly available from "http://www.iana.org/assignments/lang-subtags-templates/" each registration form. Note that multiple registrations can pertain to the same record in the registry.
Developers who are dependent upon the language subtag registry sometimes would like to be informed of changes in the registry so that they can update their implementations. When any change is made to the language subtag registry, IANA will send an announcement message to "email@example.com" (a self-subscribing list that only IANA can post to).
The Language Tag Extensions Registry can contain at most 35 records and thus changes to this registry are expected to be very infrequent.
Future work by IANA on the Language Tag Extensions Registry is limited to two cases. First, the IESG MAY request that new records be inserted into this registry from time to time. These requests MUST include the record to insert in the exact format described in Section 3.7 (Extensions and the Extensions Registry). In addition, there MAY be occasional requests from the maintaining authority for a specific extension to update the contact information or URLs in the record. These requests MUST include the complete, updated record. IANA is not responsible for validating the information provided, only that it is properly formatted. It should reasonably be seen to come from the maintaining authority named in the record present in the registry.
Language tags used in content negotiation, like any other information exchanged on the Internet, might be a source of concern because they might be used to infer the nationality of the sender, and thus identify potential targets for surveillance.
This is a special case of the general problem that anything sent is visible to the receiving party and possibly to third parties as well. It is useful to be aware that such concerns can exist in some cases.
The evaluation of the exact magnitude of the threat, and any possible countermeasures, is left to each application protocol (see BCP 72 (Rescorla, E. and B. Korver, "Guidelines for Writing RFC Text on Security Considerations," July 2003.) [RFC3552] for best current practice guidance on security threats and defenses).
The language tag associated with a particular information item is of no consequence whatsoever in determining whether that content might contain possible homographs. The fact that a text is tagged as being in one language or using a particular script subtag provides no assurance whatsoever that it does not contain characters from scripts other than the one(s) associated with or specified by that language tag.
Since there is no limit to the number of variant, private use, and extension subtags, and consequently no limit on the possible length of a tag, implementations need to guard against buffer overflow attacks. See Section 4.3 (Length Considerations) for details on language tag truncation, which can occur as a consequence of defenses against buffer overflow.
Although the specification of valid subtags for an extension (see Section 3.7 (Extensions and the Extensions Registry)) MUST be available over the Internet, implementations SHOULD NOT mechanically depend on it being always accessible, to prevent denial-of-service attacks.
The syntax in this document requires that language tags use only the characters A-Z, a-z, 0-9, and HYPHEN-MINUS, which are present in most character sets, so the composition of language tags should not have any character set issues.
Rendering of characters based on the content of a language tag is not addressed in this memo. Historically, some languages have relied on the use of specific character sets or other information in order to infer how a specific character should be rendered (notably this applies to language- and culture-specific variations of Han ideographs as used in Japanese, Chinese, and Korean). When language tags are applied to spans of text, rendering engines sometimes use that information in deciding which font to use in the absence of other information, particularly where languages with distinct writing traditions use the same characters.
The main goal for this revision of this document was to incorporate ISO 639-3 and its attendant set of language codes into the IANA Language Subtag Registry, permitting the identification of many more languages and dialects than previously supported.
The specific changes in this document to meet these goals are:
|International Organization for Standardization, "ISO 15924:2004. Information and documentation -- Codes for the representation of names of scripts," January 2004.
|International Organization for Standardization, "ISO 3166-1:2006. Codes for the representation of names of countries and their subdivisions -- Part 1: Country codes," November 2006.
|International Organization for Standardization, "ISO 639-1:2002. Codes for the representation of names of languages -- Part 1: Alpha-2 code," 2002.
|International Organization for Standardization, "ISO 639-2:1998. Codes for the representation of names of languages -- Part 2: Alpha-3 code, first edition," 1998.
|International Organization for Standardization, "ISO 639-3:2007. Codes for the representation of names of languages -- Part 3: Alpha-3 code for comprehensive coverage of languages," 2007.
|International Organization for Standardization, "ISO/IEC 646:1991, Information technology -- ISO 7-bit coded character set for information interchange.," 1991.
|Bradner, S., "The Internet Standards Process -- Revision 3," BCP 9, RFC 2026, October 1996 (TXT).
|Hovey, R. and S. Bradner, "The Organizations Involved in the IETF Standards Process," BCP 11, RFC 2028, October 1996 (TXT, HTML, XML).
|Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels," BCP 14, RFC 2119, March 1997 (TXT, HTML, XML).
|Alvestrand, H., "IETF Policy on Character Sets and Languages," BCP 18, RFC 2277, January 1998 (TXT, HTML, XML).
|Narten, T. and H. Alvestrand, "Guidelines for Writing an IANA Considerations Section in RFCs," BCP 26, RFC 2434, October 1998 (TXT, HTML, XML).
|Carpenter, B., Baker, F., and M. Roberts, "Memorandum of Understanding Concerning the Technical Work of the Internet Assigned Numbers Authority," RFC 2860, June 2000 (TXT).
|Klyne, G., Ed. and C. Newman, "Date and Time on the Internet: Timestamps," RFC 3339, July 2002 (TXT, HTML, XML).
|Ewell, D., "Initial Language Subtag Registry," RFC 4645, September 2006 (TXT).
|Phillips, A. and M. Davis, "Matching of Language Tags," BCP 47, RFC 4647, September 2006 (TXT).
|Crocker, D. and P. Overell, "Augmented BNF for Syntax Specifications: ABNF," STD 68, RFC 5234, January 2008 (TXT).
|Freitag, A., "Unicode Standard Annex #14: Line Breaking Properties," August 2006.
|Statistics Division, United Nations, "Standard Country or Area Codes for Statistical Use," UN Standard Country or Area Codes for Statistical Use, Revision 4 (United Nations publication, Sales No. 98.XVII.9, June 1999.
|Alvestrand, H., "Tags for the Identification of Languages," RFC 1766, March 1995 (TXT).
|Moore, K., "MIME (Multipurpose Internet Mail Extensions) Part Three: Message Header Extensions for Non-ASCII Text," RFC 2047, November 1996 (TXT, HTML, XML).
|Freed, N. and K. Moore, "MIME Parameter Value and Encoded Word Extensions: Character Sets, Languages, and Continuations," RFC 2231, November 1997 (TXT, HTML, XML).
|Hoffman, P. and F. Yergeau, "UTF-16, an encoding of ISO 10646," RFC 2781, February 2000 (TXT).
|Alvestrand, H., "Tags for the Identification of Languages," RFC 3066, January 2001 (TXT).
|Rescorla, E. and B. Korver, "Guidelines for Writing RFC Text on Security Considerations," BCP 72, RFC 3552, July 2003 (TXT).
|Yergeau, F., "UTF-8, a transformation format of ISO 10646," STD 63, RFC 3629, November 2003 (TXT).
|Phillips, A. and M. Davis, "Tags for Identifying Languages," BCP 47, RFC 4646, September 2006 (TXT).
|Davis, M., "Unicode Technical Standard #35: Locale Data Markup Language (LDML)," December 2007.
|Unicode Consortium, "The Unicode Consortium. The Unicode Standard, Version 5.0, (Boston, MA, Addison-Wesley, 2003. ISBN 0-321-49081-0)," January 2007.
|ISO 639 Joint Advisory Committee, "ISO 639 Joint Advisory Committee: Working principles for ISO 639 maintenance," March 2000.
|Raymond, E., "The Art of Unix Programming," 2003.
|Ewell, D., Ed., "Update to the Language Subtag Registry," September 2006.
Any list of contributors is bound to be incomplete; please regard the following as only a selection from the group of people who have contributed to make this document what it is today.
The contributors to RFC 4646, RFC 4647, RFC 3066, and RFC 1766, the precursors of this document, made enormous contributions directly or indirectly to this document and are generally responsible for the success of language tags.
The following people contributed to this document:
Stephane Bortzmeyer, Karen Broome, Peter Constable, John Cowan, Martin Duerst, Frank Ellerman, Doug Ewell, Deborah Garside, Marion Gunn, Kent Karlsson, Chris Newman, Randy Presuhn, Stephen Silver, and many, many others.
Very special thanks must go to Harald Tveit Alvestrand, who originated RFCs 1766 and 3066, and without whom this document would not have been possible.
Special thanks go to Michael Everson, who served as the Language Tag Reviewer for almost the entire RFC 1766/RFC 3066 period, as well as the Language Subtag Reviewer since the adoption of RFC 4646.
Special thanks also to Doug Ewell, for his production of the first complete subtag registry, his work to support and maintain new registrations, and his careful editorship of both RFC 4645 and [registry‑update] (Ewell, D., Ed., "Update to the Language Subtag Registry," September 2006.).
Simple language subtag:
- de (German)
- fr (French)
- ja (Japanese)
- i-enochian (example of a grandfathered tag)
Language subtag plus Script subtag:
- zh-Hant (Chinese written using the Traditional Chinese script)
- zh-Hans (Chinese written using the Simplified Chinese script)
- sr-Cyrl (Serbian written using the Cyrillic script)
- sr-Latn (Serbian written using the Latin script)
- zh-Hans-CN (Chinese written using the Simplified script as used in mainland China)
- sr-Latn-RS (Serbian written using the Latin script as used in Serbia)
sl-rozaj (Resian dialect of Slovenian)
sl-nedis (Nadiza dialect of Slovenian)
de-CH-1901 (German as used in Switzerland using the 1901 variant [orthography])
sl-IT-nedis (Slovenian as used in Italy, Nadiza dialect)
- hy-Latn-IT-arevela (Eastern Armenian written in Latin script, as used in Italy)
- de-DE (German for Germany)
- en-US (English as used in the United States)
- es-419 (Spanish appropriate for the Latin America and Caribbean region using the UN region code)
Private use subtags:
- de-CH-x-phonebk
- az-Arab-x-AZE-derbend
Private use registry values:
- x-whatever (private use using the singleton 'x')
- qaa-Qaaa-QM-x-southern (all private tags)
- de-Qaaa (German, with a private script)
- sr-Latn-QM (Serbian, Latin-script, private region)
- sr-Qaaa-RS (Serbian, private script, for Serbia)
Tags that use extensions (examples ONLY: extensions MUST be defined by revision or update to this document or by RFC):
- en-US-u-islamCal
- zh-CN-a-myExt-x-private
- en-a-myExt-b-another
Some Invalid Tags:
- de-419-DE (two region tags)
- a-DE (use of a single-character subtag in primary position; note that there are a few grandfathered tags that start with "i-" that are valid)
- ar-a-aaa-b-bbb-a-ccc (two extensions with same single-letter prefix)
LANGUAGE SUBTAG REGISTRATION FORM 1. Name of requester: Han Steenwijk 2. E-mail address of requester: han.steenwijk @ unipd.it 3. Record Requested: Type: variant Subtag: biske Description: The San Giorgio dialect of Resian Description: The Bila dialect of Resian Prefix: sl-rozaj Comments: The dialect of San Giorgio/Bila is one of the four major local dialects of Resian 4. Intended meaning of the subtag: The local variety of Resian as spoken in San Giorgio/Bila 5. Reference to published description of the language (book or article): -- Jan I.N. Baudouin de Courtenay - Opyt fonetiki rez'janskich govorov, Varsava - Peterburg: Vende - Kozancikov, 1875.
LANGUAGE SUBTAG REGISTRATION FORM 1. Name of requester: Jaska Zedlik 2. E-mail address of requester: jz53 @ zedlik.com 3. Record Requested: Type: variant Subtag: tarask Description: Belarusian in Taraskievica orthography Prefix: be Comments: The subtag represents Branislau Taraskievic's Belarusian orthography as published in "Bielaruski klasycny pravapis" by Juras Buslakou, Vincuk Viacorka, Zmicier Sanko, and Zmicier Sauka (Vilnia-Miensk 2005). 4. Intended meaning of the subtag: The subtag is intended to represent the Belarusian orthography as published in "Bielaruski klasycny pravapis" by Juras Buslakou, Vincuk Viacorka, Zmicier Sanko, and Zmicier Sauka (Vilnia-Miensk 2005). 5. Reference to published description of the language (book or article): Taraskievic, Branislau. Bielaruskaja gramatyka dla skol. Vilnia: Vyd. "Bielaruskaha kamitetu", 1929, 5th edition. Buslakou, Juras; Viacorka, Vincuk; Sanko, Zmicier; Sauka, Zmicier. Bielaruski klasycny pravapis. Vilnia-Miensk, 2005. 6. Any other relevant information: Belarusian in Taraskievica orthography became widely used, especially in Belarusian-speaking Internet segment, but besides this some books and newspapers are also printed using this orthography of Belarusian.
|Addison Phillips (editor)
|Mark Davis (editor)
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