1. A method for updating the vocabulary of a speech translation system for translating a first language into a second language, the method comprising: receiving, by at least one microphone of the speech translation system, an utterance from a user of the speech translation system, wherein the speech translation system is for translating the utterance from the first language into the second language and outputting an audible translation of the utterance in the second language from at least one speaker of the speech translation system; after receiving the utterance, receiving, from a user of the speech translation system, via a user interface of the speech translation system, an indication to add a new word in the first language to a first recognition lexicon of the first language of an automatic speech recognition module of the speech translation system, wherein the automatic speech recognition module for the speech translation system comprises the first recognition lexicon, an acoustic model for the first language, and a language model for the first language, and wherein the new word is not contained in the first recognition lexicon, the acoustic module, and the language model of the first language; determining, by the speech translation system, word class information, a pronunciation in the first language, and a translation in the second language for the new word; adding, by the speech translation system, the new word, along with the word class information and the pronunciation in the first language determined by the speech translation system, to the first recognition lexicon of the first language of the speech translation system; adding, by the speech translation system, the new word, along with the word class information and the translation in the second language determined by the speech translation system, to a first machine translation module associated with the first language of the speech translation system, wherein the first machine translation module contains a first tagging module, a first translation model and a first language module, and is configured to translate the new word to a corresponding translated word in the second language.