I had the same problem, and I wrote the following front-end only library that wraps up the code for multiple browsers. It's not much code, but nice to not have to copy and paste the same code across multiple websites.
Get it: acceptedlanguages.js
Use it:
It always returns an array, ordered by users preference. In Safari & IE the array is always single length. In FF and Chrome it may be more than one language.
