I am having the same problem here.
I live in Brazil, where the language is Portuguese but many translated menus are so poorly translated, that I prefer to run all my devices in English.
The problem is even worse, because I don't even have to reboot the phone - it changes the language to Portuguese after a few hours, without warning. I switch it on and the language has changed! Is there any thing related to the "time zone" you set the phone when you first install it? How can I circunvent this "feature"?