1. A computer system adapted to synthesize a sentence into an output language, comprising: a lexical synthesizer adapted to perform a lexical selection on the language-independent semantic structure of the sentence using lexical descriptions and semantic descriptions in the output language; a surface structure builder adapted to build a surface structure of the output sentence in the output language from the language-independent semantic structure using syntactic descriptions and morphological descriptions of the output language; and a morphological synthesizer adapted to perform a morphological synthesis on the surface structure of the output sentence in the output language using morphological descriptions of the output language and to construct the sentence in the output language.