i don't know of anything inside a programming language, but if your just trying to translate a site real quick you could just copy and past the text into a translator such as the one offered for free on altavista.com
there are php scripts that do this, there is one in the phpNuke and PostNuke system, you just have to install the new languages. I think. But really I don't know, this is just an assumption.
That just tells the browser what language to display the content in. Cause just because some japanese guy writes some stuff on a webpage, doesn't mean you'll see it in japenese characters. You have to have that language installed for your browser and you must have the proper meta tags to tell the browser to use it.