Check out Google's AJAX Language API
http://code.google.com/apis/ajaxlanguage/
If what you are wanting is Machine Translation, then I recommend this or a similar solution.
And here's another more general link: http://googlesystem.blogspot.com/2008/03/google-launched-another-ajax-api-this.html
as Amit mentioned about Translation accuracy, for langauges that have a close grammatical mapping (English <=> Spanish) or (Japanese <=> Korean) you will obtain optimal translations, which will still fall short of any human translation, but should at least be understandable. Though (English <=> Japanese) for example, provides, in my opinion a very rough, and sometimes not understandable translations. Though It should suffice in most cases.
Note: If you are trying to make a multi-lingual website, you should probably set up a different infrastructure. And consider having humans Translate the text for you: Here is a quick and simple example I whipped up in the past for creating a multi-lingual website that uses associate arrays to store your "language pack" (could also use defines) http://ken-soft.com/?p=6, and another that is 100% Database backed. http://ken-soft.com/?p=496 (you could also mix them and have your database backed language packs exported into language files as in the first link I gave. (I will be doing a massive update to this sometime this week, so stay tuned, and ask me if you have any questions, also make note that the first link is probably more useful to most people)