Make sure the xhtml is saved in utf8 format. In eclipse, you right click on the file->Properties->Resources->Text File properties and set it to utf8.
Even better is to right click on the project and force all files to be saved in utf8.
Thanks for your reply.
My project's standard encoding is not UTF-8 but GBK. If I add <?xml version=
GBK?> at the begin of the xhtml, it works. But not all xhtml accept this declaring. If I added it in the menu.xhtml, it cause error. If I don't add it, I can not type Chinese in it.