1. A method for creating or updating parallel corpus in a machine translation system, comprising the steps of: without parallel corpus, translating a test set E from a first collection to a second collection so as to create a set F in the second collection, and translating the set F from the second collection to the first collection so as to create a set E′ in the first collection, wherein differences between E and E′ are determined; computing confidence scores for a translation of each item in the test set E based on a similarity of E and E′; and based on the confidence scores, adding translations to the parallel corpus, wherein the parallel corpus is stored in memory on the machine translation system.