Facebook is working on this application internally - Facebook Translations:

http://www.facebook.com/translations/

“The Translations application by Facebook allows translators all over the world to translate Facebook into different languages. Join our community of translators and make Facebook available to everyone, everywhere, in all languages.

Currently the Facebook Translations Application is limited to beta users only. We’ll let you know when the application is available for you to use. “

It’s a really interesting idea. I am sure Facebook will pull it off nicely.
Now it’s time for translation to meet social graph.

Facebook not only can use this to translate their own applications, but also offer services to 3rd party apps - those money-hungry individual Facebook app developers. It’s a great value-add, and another good reason to grow with Facebook.

Here is my idea of Social Translation:

1. Push content to social graph

2. Filter it through social translation process

3. Evaluate it through social review process

4. Validate it through professional proofreading service (optional - depending on sensitivity of content)

5. Push to live

* Please note that I left out any engineering effort - I18N, L10n, QA, etc.