Automatic message translation in Gmail

This new feature is available to individual Gmail users as well as users of Google Apps. It’s expected to simplify communications among people who speak different languages and should make it easier for organisations who do business in different countries to communicate efficiently with partners and customers. The machine translation technology is not perfect but it should be adequate for users to get the gist of any conversation..

You can turn the feature on by going to the settings menu and clicking the Labs tab.

Gmail blog here