How to add language support?

[msck9@mizzou.edu]

Dear all, 
 Happy new year. 
 I have already installed Sarge, now I want to add some other language,
 especially Chinese. I searched the web and found to use: "apt-get
 install task-chinese-s". But unfortunately it doesn't work. When I
 login, I use gdm. I can choose "kde" or "gnome", in the language item,
 I only have "English", I have no other options.

 So in summary, how can I add other language support after I have
 installed debian already. (I know when we install it, we can choose
 what languages you want to install.)

 Thanks,
 Ming