1. A method performed by a computing system for selecting a preferred machine translation of a content item, comprising: generating multiple computer-generated translations of the content item, each of the multiple computer-generated translations of the content item created in a specified target language; providing a first computer-generated translation of the multiple computer-generated translations of the content item to a first group of users; receiving, from each of the users in the first group of users, feedback on the first computer-generated translation indicating a perceived accuracy of the first computer-generated translation; assigning a first aggregate score to the first computer-generated translation in response to the received feedback from each of the users in the first group of users; providing a second computer-generated translation of the multiple computer-generated translations of the content item to a second group of users; receiving, from each of the users in the second group of users, feedback on the second computer-generated translation indicating a perceived accuracy of the second computer-generated translation; assigning a second aggregate score to the second computer-generated translation in response to the received feedback from each of the users in the second group of users; computing that the first aggregate score is higher than the second aggregate score; in response to the computing that the first aggregate score is higher, selecting, as the preferred machine translation, the first computer-generated translation; and providing the preferred machine translation in response to subsequent requests for translations of the content item.