I'm running PHP Version 5.2.14 and I've read, at http://andrewkandels.com/my-top-ten-internationalization-headaches-and-how-i-fixed-them/ (point 7), that PHP 5 can trim some UTF-8 characters. Might this be the problem? It's next to impossible for me to know, as I don't know much about PHP, let alone the studd used to build WordPress.
If you need more details, I've included Chinese in my themes index.php and style.css files. Both are getting scrambled and I get stuff like ˮƽ���м��� instead. You can see the problem next to my titles on http://englishcollective.org/zh-hans/.