Accept-Language still cause quite a bit annoyance to me though. Because the fallback rule most implements still follows similar assumption as the first point in this article. Languages in the same group doesn't mean the user would accept it.
I don't care if there are any other auto-translated thing that you though it's close enough because they have same prefix that would help.
NO, absolutely NO.
I even specified the en-US or any other language that original content uses as the secondary candidates, then most just ignores it and serves randomly translated thing that you think would be close enough because you can't tell.
Surely, even using an extension mainly to hide these stuffs.
Not only mirroring SO, also its siblings (like serverfault and askubuntu), and others like GitHub.
But the most annoying part is it keeps showing those mirrored and machine translated stuffs that offers little to none benefits to me and I'm already being forced trained enough to identify those at first glance.
Those even shows up when I'm already searching in other languages, ahrr.