That's exactly what should happen, the problem is a lot of sites don't do that. I'm US, living in Vietnam and half the time the Facebook login screen turns up with Vietnamese and no way to change the language. If anything, this forced me to learn those 'login' words in Vietnamese.
I'm British and also living in Vietnam currently, and this has also been my experience. Also, if I'm in Thailand all the Google search results are returned with timestamps converted to Buddhist calendar years. Genius.
Is it unreasonable of me to be less tolerant of this brokenness when it comes from companies with all the money in the world, and also all the highest paid developers in the world?
Imagine being able to invert a binary tree on a whiteboard, but not being able to follow a basic HTTP specification. Insane.
I can confirm having the exact same issue, Facebook isn't alone though. Google also tries to be clever and fails hard. There's only one way to get the preferred user language, it's to check the Accept-Language header, anything else will fail, please don't try to be clever.
