I was helping someone install the simplified Chinese language in KDE the other day. After installing the kde-i18n Chinese and Simplified Chinese language packs for KDE we installed the fonts-chinese pack for CentOS. Then we went to turn on the new language. Open Control Center -> Regional and Accessibility -> Country/Region & Language. We Selected Add Language, select Chinese or Simplified Chinese. Clicked Apply. Most of the characters looked like little boxes (squares). I'm no world traveler but I do know Chinese characters are not all boxes.
After searching all settings and making sure all the packages for Chinese fonts for the OS and for KDE are installed I found out the problem. You have to change the font type to Sans Serif or another mono spaced font. The little boxes go away after that.
Here's a little suggestion for the KDE developers. If a font for a language needs to be mono space let's try to switch to a mono space font when the language that needs it is selected.
I did find any easy way to install all the Chinese language support on CentOS. Just use the following command.
yum groupinstall "Chinese Support"