Here are your options:
1. You could get AppLocale (select your game, and select either the third or second-to-last option on the language bar; get AppLocale on the "Technical Difficulties" page.
2. Change your system locale to Chinese Simplified PRC. To do that, go to the Control Panel on the Start Menu, select "Change keyboards or other input methods", click on "Change system locale" and select Chinese Simplified PRC on the language bar. You'll have to restart your computer if you click OK.