The actual mechanism your User Agent tells the server which languages you are interested in is even more robust [0] ! It is a weighted list of preferences.

The reasons I've heard from web developers on why they don't use this is because they believe that the user probably never set that up right, and that multiple people could be using the web browser so they need to be able to do the right thing.

What I typically do is select the best matching language from the Accept-Language HTTP header, and then override it with a session-specific value IF one is supplied. Example:

1. https://rkeene.org/projects/6to4/

2. https://rkeene.org/projects/6to4/?lang=fr

You can see PART of the problem here from the web developers perspective. This isn't a negotiation so you have no way to know which languages the server supports. If your preferences aren't totally inclusive you'll get something "wrong". This can be solved by exposing that information (as not done above) and allowing the user to override it (as above).

[0] https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Ac...

The problem is that every big website operator wants to make it work correctly for you, and they (1) have different definitions for success and (2) assume you're incompetent.

In the first point, there's someone with a requirements document that assumes every country has one official language and everyone in that country speaks that language, and so feels successful and internationalization-ready when a geo-IP served page is automatically switched to the "correct" language (much like "Falsehoods programmers believe about names").

Second, configuring a computer's locale to set a browser's request headers correctly is beyond the technical expertise of many users. It would be better if things were consistent, but at the point where some locales were set incorrectly and some were uniquely set intentionally your analytics would have showed that you improved the situation on average by trying to guess the locale (screwing over users who knew how to use their computer) than by respecting it and eventually getting everyone to understand how to set their desired language.

if you install a hungarian firefox, the accept language header will reflect this (or it did when i tried it last time). Non-expert users also often choose software in their language mutation. I dont have numbers but i wouldnt be surprised if a lot of browsers were sending correct accept language headers.

i dont know IE but it was in a very good position to guess the language of the user as well.

Agreed, but then they should give the users a way of overriding that. Google in particular knows what users want because they force you to answer it when you create your account. I've set every single location setting to UK, and yet when I travel abroad they insist of ignoring it. No excuse there.