Apple has released an update to Mountain Lion, 10.8.1, which includes a fix to "Address an issue that could cause the system to become unresponsive when using Pinyin input". http://support.apple.com/kb/HT5418
Many users are finding that after upgrading to OS X 10.8 Mountain Lion, the service for converting between Traditional and Simplified Chinese no longer works. For a fix see this post in the Apple Support Community.