The South Slavic languages are one of three branches of the Slavic languages. There are approximately 30 million speakers, mainly in the Balkans. These are separated geographically from speakers of the other two Slavic branches (West and East) by a belt of German, Hungarian and Romanian speakers. History The first South Slavic language to be written (also the first attested Slavic language) was the variety of the Eastern South Slavic spoken in Thessaloniki, now called Old Church Slavonic, in the ninth century. It is retained as a liturgical language in Slavic Orthodox churches in the form of various local Church Slavonic traditions. Classification The South Slavic languages constitute a dialect continuum. Serbian, Croatian, Bosnian, and Montenegrin constitute a single dialect within this continuum. Eastern Bulgarian – (ISO 639-1 code: bg; ISO 639-2 code: bul; SIL code: bul; Linguasphere: 53-AAA-hb) Macedonian – (ISO 639-1 code: mk; ISO 639-2(B) code: mac; ISO 639-2(T) code: mkd; SIL code: mkd; Linguasphere: 53-AAA-ha) Old Church Slavonic (extinct) – (ISO 639-1 code: cu; ISO 639-2 code: chu; SIL code: chu; Linguasphere: 53-AAA-a) Transitional Torlakian Slovene (ISO 639-1 code: sl; ISO 639-2 code: slv; ISO 639-3 code: slv; Linguasphere: 53-AAA-f) Kajkavian (ISO 639-3 code: kjv) Chakavian (ISO 639-3 code: ckm) Serbo-Croatian/Shtokavian (ISO 639-1 code: sh; ISO 639-2/3 code: hbs; SIL code: scr; Linguasphere: 53-AAA-g).There are four national standard languages based on the Eastern Herzegovinian dialect: Serbian (ISO 639-1 code: sr; ISO 639-2/3 code: srp; SIL code: srp) Croatian (ISO 639-1 code: hr; ISO 639-2/3 code: hrv; SIL code: hrv) Bosnian (ISO 639-1 code: bs; ISO 639-2/3 code: bos; SIL code: bos) Montenegrin (ISO 639-2/3 code: cnr; SIL code: cnr) Linguistic prehistory The Slavic languages are part of the Balto-Slavic group, which belongs to the Indo-European language family. The South Slavic languages have been considered a genetic node in Slavic studies: defined by a set of phonological, morphological and lexical innovations (isoglosses) which separate it from the Western and Eastern Slavic groups. That view, however, has been challenged in recent decades (see below). Some innovations encompassing all South Slavic languages are shared with the Eastern Slavic group, but not the Western Slavic. These include: Consistent application of Slavic second palatalization before Proto-Slavic *v Loss of *d and *t before Proto-Slavic *l Merger of Proto-Slavic *ś (resulting from the second and third palatalization) with *s This is illustrated in the following table: Several isoglosses have been identified which are