This is not the 1st time the question has been raised here, and it seems like you couldn't use anything else than regular ASCII characters in the 3D text tool until Blender 2.4.x.
But it seems like things have evolved in Blender 2.5.x and now you can actually use accented characters. So, I tried to input Chinese characters in the Windows 2.5.6a version but to no avail. I first change the font to Arial Unicode, then tried first by direct input using regular Windows IME, then by copy-pasting from MS Word 2010.
Nothing worked at all. Then I tried to copy-paste several characters, even the simple one like a regular "e", nothing worked. It seems like the paste button of the text edit group in the text edit panel doesn't work.
Just tried the same things with no luck.
You might already know about this, but using Inkscape
to type your text and then convert the text into curves, you can then import the .SVG file into blender as curves.
So far this is the only usable solution that I could find. Here is the tutorial that I stumbled on http://www.5xj.com/blender/ILoveYou.html
But it would be nice if anyone knows how to use the built in 3d text tools to input Chinese
Blender 2.64 (Linux) can type Chinese characters with the 3D text tool now.
And can rename Chinese characters for the objects in Outline deitor too. Ubuntu 12.04, Ibus Pinyin is work well.
( Windows system still can not yet.)