it depends on what mod it is = which file is modded...
Some mods can be translated by modding the other language file the same way the english one was made
some mods can be translated by using the rsc editor and translating the strings by hand
some mods, which are ports from other firmware's can be translated by getting the files from the firmware it was ported from....
As you see, it is different from mod to mod, as file to file
post your mod here and i will explain what to do
or maybe I already have a translation and I can post it
I'll make a couple threads explaining what I do