The German language is interspersed with words, mostly foreign words, which cannot be converted correctly by German grapheme-to-phoneme rules. Almost all of these words belong to the English or French language. In order to convert the whole text correctly, it is necessary to identify the language of each word and then to use the corresponding set of grapheme-to-phoneme rules. The problem of language identification is centrally important for almost every application of automatic text output when its source is a multilingual text database.
Bibliographic reference. Henrich, Peter (1989): "Language identification for the automatic grapheme-to-phoneme conversion of foreign words in a German text-to-speech system", In EUROSPEECH-1989, 2220-2223.