[CentOS] How to add a language to the system?

Hi,

A quick question, I hope...

I have performed a complete package installation on CentOS 4, and upon 
installing it, as languages I chose English US and English UK.

However... As I also write in Dutch and in Spanish, I need to install 
these languages as special characters like the 'enye' (= an 'n' with a 
'tilde' over it) are currently missing from my system...

Now, I checked the 'System settings' menu and it only seems to allow me 
to change the default language, but I do not see where I can install 
additional languages.

Can anyone tell me how to go about this?

Cheers!
Olafo