Okay, so here is the result of some experimentation that is unfortunately limited to cemu since I don't have a Wii U.
For some reason perhaps because the language is not supported but using this current method to add English text to the Japanese game will crash cemu, it's probably a cemu problem but since no one has tried it on the Wii U, I don't know if this will happen on the console as well. Using the old method or just loading up the Japanese game without any changes will play normally so there definitely is something incompatible here.
I'm sure it is possible to undub the game, we just haven't found it yet.
I tried it, but the game crashes (in fact, the wii u freezes after the splash screen and the little music) but i see there is a font file, maybe we have to transfer it as well ?