Methods, systems, and apparatus, including computer program products, operable to perform operations including receiving from a user through a user interface a search query comprising a query term, the search query having attributed to it a query language; deriving a simplified query term from the query term; and identifying one or more potential synonyms for the query term by looking up the simplified query term in a synonyms map, the synonyms map mapping each of a plurality of keys to one or more corresponding variants, each variant being a word associated with one or more document languages, and each variant being associated for each associated language with a variant-language score indicating a relative frequency of the variant among all variants for the associated language for the same key.