11. A system comprising: a non-transitory computer readable medium having instructions stored thereon; and a data processing apparatus configured to execute the instructions to perform operations comprising: obtaining, from a client device of a user, a text message in a first language, the text message comprising at least one word; providing the text message to a machine translation system; obtaining a translation of the text message from the machine translation system; determining that the text message and the translation both comprise the at least one word in the first language and that the at least one word is correctly spelled; and performing one or more of the following: (a) determining Bayesian probabilities for neighboring words that appear before and after the at least one word and, when the Bayesian probabilities exceed a threshold value, adding the at least one word to a lexicon in a data store; and (b) performing k-means clustering to identify a cluster of words comprising synonyms and, when the cluster comprises the at least one word, adding the at least one word to the lexicon in the data store.
11. A system comprising: a non-transitory computer readable medium having instructions stored thereon; and a data processing apparatus configured to execute the instructions to perform operations comprising: obtaining, from a client device of a user, a text message in a first language, the text message comprising at least one word; providing the text message to a machine translation system; obtaining a translation of the text message from the machine translation system; determining that the text message and the translation both comprise the at least one word in the first language and that the at least one word is correctly spelled; and performing one or more of the following: (a) determining Bayesian probabilities for neighboring words that appear before and after the at least one word and, when the Bayesian probabilities exceed a threshold value, adding the at least one word to a lexicon in a data store; and (b) performing k-means clustering to identify a cluster of words comprising synonyms and, when the cluster comprises the at least one word, adding the at least one word to the lexicon in the data store. 15. The system of claim 11 , wherein the user is a player in an online game.