It's definatately a good idea to setup a test board - do all your modificatiosn and make sure it works - then move it over to your real board and alter your database.
The language files have been updated quite a bit since 6.02. So you'll want to start fresh - or compare them to add all the new langague strings. The whole admin section has been added to language files too.
Threads does offer the ability to add/create languages on the fly from the admin menu - as well as choose the charset etc... so maybe it'll be easier. But I think the files have changed enough that you'll need to start fresh.
