I don't know what kind of type you are using, but if you are using Roman pin ying/han zi (漢字) or zhu yin(注音), I suggest you to visit this website http://uao.cpatch.org/index.php?%E4%B8%8B%E8%BC%89 and download the unicode for you computer, after install restart your computer, and set up you language bar for the key input, you can use both also english. Usually I am using shift+ctrl to change the type it works inside and outside WOW. You will see the Chinese(traditional,taiwan) on your right bottom screen, find "Tool Menu" icon, click and choose "Properties", find "keyboard" tab and you will see "choose your prefeered keyboard layout".
choose "Han Yu Pinyin" for Roman type ( mama : 媽媽 ) or
"Ching Yeah" for Zhu Yin type ( ㄇㄚㄇㄚ :媽媽 )
note: if you are using Win 7 you can install the language's
typing without install Unicode 2.50, anyway I hope this
can solve your problem, and understand my English