Hi guys, I have an alternative suggestion for you.

There is also a gettext implementation for javascript. It works very nicely for us.
Apparently it also has a sprintf like support, but I haven’t tested it yet.

I’ve written a blog post about it: http://wallsoft.blogspot.com/2008/01/gettext-for-php-and-javascript.html

The library can be found here: http://code.google.com/p/gettext-js/