Abstract: A method for building a multilingual translation database system includes the steps of: providing a plurality of multilingual sentence pairs or multilingual sentence-fragment pairs in a translation database, each of the multilingual sentence pairs or the multilingual sentence-fragment pairs formed with a source language and a target language; selecting repeated sentence structures or repeated sentence fragments from the multilingual sentence pairs or the multilingual sentence-fragment pairs; and defining or qualifying at least one repeated key sentence or key sentence fragment of the repeated sentence structures or the repeated key sentence-fragment structures with a predetermined degree of repeat frequency.