On the same tab, click on Details, then on the new window, under the Preferences section of the Settings tab, click on Language Bar, then check Show the Language bar on the desktop. If you have not added the Chinese input before, you can do so at Installed Services section of the same window.
Click Add and choose the input language you desire. I would let the screenshot do the rest of the talking.
http://dl.latecomerx.com/images/Screenshot_2007-09-08_08-48-47.jpeg