4
You need to have several language folders for your language to show in your whole site:
1. For Core language: xoops_url/language/[your language]/
2. For Module language: xoops_url/modules/[modulename]/language/[your language]/ for every module.
If you can't find a translation for a module you use, then you might have to make one yourself. That would mean copying the english folder for the module, changing the name to the name of your language, and changing all the english language values to your language.
e.g.
define("_NOCOMMENTS","No Comments");
will become:
define("_NOCOMMENTS","Whatever you want here");
I found one thread
where someone had translated the core language to Vietnamese. (I'm assuming it was the Vietnamese language you were looking for?) There are also a few good tips about translating in that thread, so it's useful even if it was another language you were after.
Good luck
Rowd