In my page I had: <html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en">
but this caused the problem that it only displays English charactors, other languages will be displayed with unrecognizable code. When I remove those attributes, it worked.
But some page with <html> only still displays unrecognizable code if other languages are used. The database has been checked to support multiple language without problem. So can someone tell me is there anywhere else in the page I should pay attention to let page support multiple languages?