In this paper we view Lexicalized Tree Adjoining Grammars as the compilation of a tract and modular layer of linguistic description :the metagrammar (MG). MG provides a hierarchical representation of lexicosyntactic descriptions and principles that capture the well-formedness of lexicalized structures, expressed using syntactic functions. This makes it possible for a tool to compile an instance of MG into an LTAG, automatically performing the relevant combinations of linguistic phenomena. We then describe the instantiation of an MG for Italian and French. The work for French was performed starting with an existing LTAG, which has been augmented as a result. The work for Italian was performed by systematic contrast with the French MG. The automatic compilation gives two parallel LTAG, compatible for multilingual NLP applications.