11. A computer program product, encoded on a computer-readable medium, operable to cause data processing apparatus to perform operations comprising: receiving data representative of a search query from a user located at a geographic location; determining a plurality of languages used at the geographic location; identifying a plurality of search results responsive to the search query, wherein each search result refers to a respective document; obtaining, for each particular search result of the plurality of search results, a group of multiple click measures that are associated with the document referred to by the particular search result, wherein: each of the multiple click measures in the group corresponds to a different language from the plurality of languages; and each of the multiple click measures in the group is a ratio of (i) a count of times that users who use the language corresponding to the click measure have selected, from search results for the query, the document referred to by the particular search result and (ii) a count of times that users who use any of the plurality of languages have selected, from search results for the query, the document referred to by the particular search result; for each of a plurality of the search results, generating a combined click measure by combining the multiple click measures associated with the document referred to by the search result; and ranking the search results based upon, at least, the combined click measures.
11. A computer program product, encoded on a computer-readable medium, operable to cause data processing apparatus to perform operations comprising: receiving data representative of a search query from a user located at a geographic location; determining a plurality of languages used at the geographic location; identifying a plurality of search results responsive to the search query, wherein each search result refers to a respective document; obtaining, for each particular search result of the plurality of search results, a group of multiple click measures that are associated with the document referred to by the particular search result, wherein: each of the multiple click measures in the group corresponds to a different language from the plurality of languages; and each of the multiple click measures in the group is a ratio of (i) a count of times that users who use the language corresponding to the click measure have selected, from search results for the query, the document referred to by the particular search result and (ii) a count of times that users who use any of the plurality of languages have selected, from search results for the query, the document referred to by the particular search result; for each of a plurality of the search results, generating a combined click measure by combining the multiple click measures associated with the document referred to by the search result; and ranking the search results based upon, at least, the combined click measures. 15. The program product of claim 11 wherein combining the multiple click measures comprises calculating a ratio of a sum of the multiple click measures and a sum of click counts for the search query.