Accept-Language is fun. I have an accept-language that orders them en, ja, other. aa.com (American Airlines) then uses that to display the content to me in English, except dates and times which always appear in Japanese (１２月２５日 午後１時１０分). Fun times.
For a while I had my system language preferences set as en-UK, ja, en-US and every so often I'd get an installation that was in Japanese because there was no UK English version.
