Sure, using the OS settings would be the most sane way, but I still see it working well 9 out of 10 times. Could be a lot better, but I don't think it deserves "taking the cake" of the localization-challenged software.
And ok, it was my fault for not testing the language option before mentioning it.
Can you clarify when you think it's a good idea to override the user's OS and browser language settings based on IP registration information? (Chrome's wording in the languages settings tab is: "Add the languages you use to read websites, listing in order of preference.")
Also, it's not "localization-challenged". I would be more sympathetic to sites in general if there was no Accept-Language header, and if geo-IP lookup was some automatic service baked into every web app library.
But no, sites doing this go out of their way to do this. It's as if there's some secret coalition of idiot PMs that think adding IP-based language settings is going to get them a bonus or something.
And ok, it was my fault for not testing the language option before mentioning it.