So for my Linux 1.001 version of the game, there was no option to change the language. I'm not sure if this is just how 1.001 is or if there's a problem. I know it's not Config.ini, I have that untouched—if that's not the problem (if there is one), then what is it?

Thank you!

Sadly, Japanese was added to Undertale in Version 1.05. You need not need to worry about Japanese gameplay - unless you are running categories V1.02+. Hope this helps.

I see. That helps now. Thank you!