1. A method comprising: receiving from a user, an utterance in a first language that is to be translated by a speech translation system from the first language to a second language; receiving, an indication to add a new word in the first language to a first recognition lexicon of the first language of a first automatic speech recognition module of the speech translation system; determining for the new word, by a processor, word class information, a pronunciation in the first language, a translation in the second language, and a pronunciation in the second language in response to receiving the indication to add the new word; adding the new word the determined word class information and the determined pronunciation in the first language to the first recognition lexicon of the first language of the first automatic speech recognition module; and adding the new word, the determined word class information, the determined translation in the second language and the pronunciation of the translation in the second language, to a first machine translation module associated with the first language of the speech translation system.