1. A computer-implemented method comprising: receiving an initial search query including one or more terms; using statistical machine translation to translate the initial search query into a translated search query, the translated search query being different from the initial search query and being in a same natural language as the initial search query; identifying a first term occurring in the initial search query that was replaced by a corresponding second term occurring in the translated search query; determining that one or more context terms occurring adjacent to the first term in the initial search query also occur adjacent to the second term in the translated search query; and in response to determining that one or more context terms occurring adjacent to the first term in the initial search query also occur adjacent to the second term in the translated search query, designating the second term as a synonym of the first term when the first term occurs adjacent to the one or more context terms in search queries, wherein a search engine expands a particular search query to include the second term in response to a determination that the first term occurs adjacent to the one or more context terms in the particular search query.