1. A method performed by data processing apparatus, the method comprising: receiving a query in a source language, the query including one or more query terms; determining one or more target languages relevant to the query using one or more language scores associated with each of the one or more query terms, wherein determining one or more target languages relevant to the query includes: identifying terms related to the query for each related term, determining a language score for each of a plurality of languages; combining the language scores for each related term for each respective language of the plurality of languages; and determining one or more target languages relevant to the query, other than the source language, as corresponding to languages of the plurality of languages having a combined language score beyond a threshold score; translating the query into one or more translated queries in the respective one or more target languages; determining search results responsive to the respective one or more translated queries; and providing one or more of the search results.