Google launched another AJAX API, this time for language detection and translation. The API works for the same language pairs that are available at Google Translate and lets you display the translation of a text inside your own page, without having to link to an external translation service.
The translation API could be used to automatically translate some content from a web page using the browser's preferred language, to create a Greasemonkey script that translates to English the posts written in other languages, to detect if a comment is written in English before posting it and for many other things.
Here's one example of use, where you can enter a text in one of the supported languages (Arabic, Chinese, French, German, Greek, Dutch, Italian, Japanese, Korean, Portuguese, Russian, Spanish), Google automatically detects the language and it shows the English translation. The sample text is from Le Monde.