5. A non-transitory computer readable media encoded with instructions that are operable, when executed by one or more computers, to cause the one or more computers to perform operations comprising: retrieving, by an information retrieval system comprising one or more computers, a group of documents over a network, each document in the group of documents being located at a respective network location; identifying links occurring in the group of documents, wherein each link occurring in the group of documents has associated anchor text and points to a network location of another document in the group of documents; translating, by one or more translation engines installed on one or more computers of the information retrieval system, each document in the group of documents into each of a plurality of target languages using a respective context-specific translation model for each of the target languages to generate a respective translated document in each target language for each of the documents in the group, wherein the context of each respective context-specific translation model depends at least in part on the anchor text of one or more of the identified links pointing to the document; translating, by one or more translation engines, into each of the target languages the anchor text of the links pointing to documents in the group to generate translated anchor texts; indexing the translated anchor texts; indexing the documents in the group and the translated documents; receiving, over the network by a search engine installed on the one or more computers of the information retrieval system, a query in a first language, the first language being one of the target languages, after the translating and indexing of the documents and the anchor texts; and searching, by the search engine, the documents in the group that are in the first language, the translated documents that are in the first language, and the translated anchor texts that are in the first language to identify documents responsive to the query.
5. A non-transitory computer readable media encoded with instructions that are operable, when executed by one or more computers, to cause the one or more computers to perform operations comprising: retrieving, by an information retrieval system comprising one or more computers, a group of documents over a network, each document in the group of documents being located at a respective network location; identifying links occurring in the group of documents, wherein each link occurring in the group of documents has associated anchor text and points to a network location of another document in the group of documents; translating, by one or more translation engines installed on one or more computers of the information retrieval system, each document in the group of documents into each of a plurality of target languages using a respective context-specific translation model for each of the target languages to generate a respective translated document in each target language for each of the documents in the group, wherein the context of each respective context-specific translation model depends at least in part on the anchor text of one or more of the identified links pointing to the document; translating, by one or more translation engines, into each of the target languages the anchor text of the links pointing to documents in the group to generate translated anchor texts; indexing the translated anchor texts; indexing the documents in the group and the translated documents; receiving, over the network by a search engine installed on the one or more computers of the information retrieval system, a query in a first language, the first language being one of the target languages, after the translating and indexing of the documents and the anchor texts; and searching, by the search engine, the documents in the group that are in the first language, the translated documents that are in the first language, and the translated anchor texts that are in the first language to identify documents responsive to the query. 8. The non-transitory computer readable media of claim 5 , wherein: translating the anchor text comprises using a web page to which the anchor text points or a web page in which the anchor text is located or both to provide context for the translation.