Hello,
I am the developer of arc_unpacker. I'm afraid that in its current form, it can be used only for resource extraction.
However, I'd be glad to help you with translating the game by developing a tool for you, that allowed putting translated text back into the game.
Since I have no experience with any translation projects, I'd need guidance regarding your expectations from the hypothetical tool's interface (for example, if you're okay with console tools or not).
Anyway, unfortunately this would need to wait until I'm done porting the Ruby code into C++, which I optimistcally presume will happen in about a week.