Automatic translation between human languages was one of the earliest applications suggested for digital computers, but it wasn't easy to do it. Machine translation generally uses natural language processing and tries to define rules for fixed constructions. The original text is encoded in a symbolic representation from which the translated text is derived.
Google developed a different kind of machine translation using a statistical approach. "We feed the computer with billions of words of text, both monolingual text in the target language, and aligned text consisting of examples of human translations between the languages. We then apply statistical learning techniques to build a translation model." explains