David Bellos in The Independent:
Using software originally developed in the 1980s by researchers at IBM, Google has created an automatic translation tool that is unlike all others. It is not based on the intellectual presuppositions of early machine translation efforts – it isn't an algorithm designed only to extract the meaning of an expression from its syntax and vocabulary. In fact, at bottom, it doesn't deal with meaning at all. Instead of taking a linguistic expression as something that requires decoding, Google Translate (GT) takes it as something that has probably been said before. It uses vast computing power to scour the internet in the blink of an eye, looking for the expression in some text that exists alongside its paired translation.
The corpus it can scan includes all the paper put out since 1957 by the EU in two dozen languages, everything the UN and its agencies have ever done in writing in six official languages, and huge amounts of other material, from the records of international tribunals to company reports and all the articles and books in bilingual form that have been put up on the web by individuals, libraries, booksellers, authors and academic departments. Drawing on the already established patterns of matches between these millions of paired documents, Google Translate uses statistical methods to pick out the most probable acceptable version of what's been submitted to it.