hmm... these are all what I did:
first, get free japanese ttf font from the internet. and copy it to SD.
then run terminal, type these in order, line by line:
cd ../usr/X11R6/lib/X11/fonts/
mkdir NewFont
cd
cd ../SD/SD_1/ (If ttf in the root of SD)
cp xxx.ttf /usr/X11R6/lib/X11/fonts/NewFont
cd
cd ../usr/X11R6/lib/X11/fonts/NewFont
mkfontscale
mkfontdir -e
fc-cache -f -v
now, xxx.ttf is copied to the folder "/usr/X11R6/lib/X11/fonts/NewFont".
then run text editor (like leafpad or something) and open "xorg.conf" at "/etc/X11/", and add this line to [Section "Files"]:
FontPath "/usr/X11R6/lib/X11/fonts/NewFont"
now, copied ttf font is registerd.
sorry for my poor explanation... I don't know decent way because I'm noob too.
I wish I could make a package to install easily.
P.S. I installed 3MX-rc2, there are probably some difference.