(Maybe you already knows)
There is a truth for Arcturus that make testing/deployment of translations very easily without re-compiling the very huge data.pak.
Arcturus will actually try to find the file on your hard disk before loading it from data.pak, i.e. If you create a file of same name in the same directory, it will be loaded instead of the copy from data.pak.
For instance, you may try to find a bmp file, rename to title.bmp, then place it in data\bmp directory and launch the game, see the result?
Hope this information helps.