In order to render japanese characters, we need to have a font which has japanese characters and make sure they
are added to the .font64 file with mkfont during compilation.
I wrote a small program before to figure out which Japanese characters are actually used in the Japanese gameboy
cartridges.
I only added those unicode ranges to the fonts to keep them small.
There was no easy way to have a font that has both latin and Japanese characters, especially not free. So I
used FontForge to merge the japanese glyphs from Osaka Regular-Mono into Arial.ttf