best practice wrt multi-lingual websites, gettext() etc.

I am writing a small(ish) site which will eventually need to be available in several different languages. This needs to more or less transparent to the user, so I am using Apaches content negotiation features, which is working very well. The issues arise once I start looking at PHP and Javascript code. I use JS for client side input (pre-)validation and increased usability, and error messages and such will obviously need to be language-sensitive. The same goes for the PHP code. With PHP, I've got gettext() for this sort of job, with javascript and some DHTML, I don't seem to have many options. One of my key concerns is - for the translation, I need to be able to wrap everything up and ship it off to a translator, perhaps via elance or similar. Does anyone have any best practice suggestions or comments in general? /Per Jessen, Zürich