17. The computer-readable storage medium of claim 10 , wherein at least one of the preferred translations is obtained by providing the source phrase to a human translator and receiving, from the human translator, the translation of the source phrase.
10. A non-transitory computer-readable storage medium storing instructions that, when executed by a computing system, cause the computing system to perform operations for improving a machine translation engine by augmenting the machine translation engine with preferred translations, the operations comprising: identifying, as low scoring content items, content items that are associated with a user rating below a content item threshold; dividing the low scoring content items into multiple n-grams; computing an overall score for each selected n-gram of the multiple n-grams by one or both of: computing a frequency that the selected n-gram appears at least once in each of the low scoring content items; or computing a frequency that the selected n-gram appears in the low scoring content items; selecting, as low scoring n-grams, at least one of the one or more n-grams that has an overall score below an n-gram score threshold; obtaining preferred translations for each of the selected low scoring n-grams, wherein each preferred translation comprises a source phrase in a first language and a translation of the source phrase in a second language; and generating the machine translation engine using training data that includes the preferred translations, wherein the preferred translations in the training data are weighted more heavily than other items in the training data that are not preferred translations.