The MT engine of the Janus speech-to-speech translation system is designed around four main principles: 1 an interlingua approach that allows the e cient addition of new languages, 2 the use of semantic grammars that yield low cost high quality translations for limited domains, 3 modular grammars that support easy expansion into new domains, and 4 e cient integration of multiple grammars using multi-domain parse lattices and domain re-scoring. Within the framework of the C-STAR-II speech-to-speech translation effort, these principles are tested against the challenge of providing translation for a number of domains and language pairs with the additional restriction of a common interchange format.