Perhaps I am wrong but in my experience Chrome, Firefox and the platform included browsers all set the browser language to the OS language by default.

While not a perfection solution I feel if the user is able to understand the language of the OS they are using then giving them a website in the same language is much better than picking one based on an IP location.

I totally agree the browser language options are hidden with a pretty crappy UI that no normal user would find and use easily.