Hmm... I'm not sure how that it works at all, currently
If I remember correctly, the internationalisation stuff is all hardcoded and only works for English and Simplified Chinese so far... the drop down list where you can select your language is not configurable. That's one of the things that we need to overwork urgently. :?
I've started working on that a few months back, but abandoned after hitting some obstacle... don't remember what it was... it wasn't so urgent then, either...
Huh... maybe with some luck, I can find it again
But, in theory, you "only" copy that file (the one where you have replaced the strings) into the folder where all the translation files are kept (somewhere deep inside the "share" folder), and it just works magically. This would of course preferrably be done by the update script too, so not something you would need to worry about.
So... what to do for now? If you have a translation, please make it available somewhere (Launchpad, or BerliOS under the category "Translation"), and have some patience. As soon as internationalisation
actually works, we'll collect all the translations that we can find.