Allow Japanese versions of mod menu text to fall back to English text

[drojf]

We have BGM/SE descriptions displayed on the in-game menu. I allocated space for a japanese description, but right now it's just a duplicated version of the English description.

This makes it annoying to edit. It would be easier if the engine detects the JP text is blank, it fills it in with the English text. At a later date, if we want to add a JP description it can be added in.

I also noticed that there are many #NOT SET# when using JP mode, which should also just display the English text (perhaps with a # at the end to indicate it's using a fallback value). I have to double check if my mod being out of date is causing this issue though.