Gmail adds email translation features: Is this helpful?
Google also has a web-based language translator. It comes in handy if you're trying to read a news item on a web site in a language you don't speak. But I'm not sure I really need this feature in my email. I don't tend to correspond with people who speak languages that I can't understand via email. But maybe that's just me. Because Google just rolled out a new Gmail labs feature that lets you add a translation button to messages in your inbox in a foreign language.
I suppose there is one area where this could be useful. If you have a friend who speaks German as their first language, but who also speaks English, you may find yourself corresponding most frequently in English. But while he might be able to keep up with a little work, he may find it easier to hit the translate button. Unfortunately, computer translations are usually bad enough that even if his English isn't great, he may find them harder to understand after they're translated.