Next delete Prerendered Item Cache in Tools -> misc and delete your cookies. I think you have got every setting. Perhaps you should also check the stub file(s) if you use any.
The idea of multiple languages is good thought of. There is a default language that everybody sees upon entering the blog (for the first time). Within this environment there can be a single post in a different language. Furtermore, registered users (bloggers) can set their personal language.
The drawback of it all is that the admin has to manage it all.

Good luck

Thank you for your answer, I have try your suggestion, but still get the same issue. I would plan to change my default language to zh-TW (Trad. Chinese).
I would send my site information to you by pm, please kindly help to make suggestion if possbile. Thank you very much!!!

P.S. I can do this setup fine in the previous version (0.9.2)

Hi windpuff,

I looked at your site and the setup is ok. What you need to do is this. From the 0.9 install pick up the language files for zh-TW and install them. Unfortunately there are no language files that are more recent. These 'old' files should work perfectly but miss a few (a lot) translations. If that is bothering, you can edit the language file yourself and translate at least the terms on the blog main page.
You find useful information on this topic [url=http://manual.b2evolution.net/Localization]here[/url].

Do try to post something in Chinese (or is it Taiwanese?) and look if the post displays correctly. If there are issues with the font being displayed, there are solutions to that.

Please keep us informed on your progress.

Good luck

Hi Afwas,

Thank you for information, it seems work on the latest version, but I got another problem :

Once I login to the system sucessful, it can display the Taiwanese content normally, but after logout, it can't display again.

P.S. I use the same setting that pm to you previously.