What should I do to use Japanese fonts in Badger 2040?
This is how I added an extra font to a Pi Pico UC. I hope it helps.
Galactic Unicorn - lower case text - Support - Pimoroni Buccaneers
You can find the bit patterns for the characters on page 14 of this publication (I think they are Japanese).
没有幻灯片标题 (waveshare.com)
Look at columns 1010 to 1101.
You quickly get into the method coding the characters into bit patterns.
I would be interested to see your results.
Best of luck
Tony