1. A computer implemented method comprising: determining, using one or more data processing apparatus, an interface language associated with a user interface through which one or more query terms of a search query are received; identifying respective languages that are associated with search result selections for a plurality of previously submitted search queries, each of the previously submitted search queries matching the search query; determining, for each identified language and based on the respective languages that are associated with the search result selections, a respective likelihood that the search query is in the language; and selecting a likelihood for a language that matches the interface language as a likelihood that one or more of the query terms are in the interface language; determining, for each of the query terms, a vector corresponding to a set of likelihoods that the respective query term is in a plurality of languages; multiplying together the vectors corresponding to the sets of likelihoods that the query terms are in the plurality of languages to generate a resultant vector; multiplying the resultant vector by the likelihood that one or more of the query terms are in the determined interface language to generate a query probability vector; and selecting a query language of the query based at least on the query probability vector.