Hello Jakub, I found documentation at http://www.twics.com/~craig/writings/linux-nihongo/ that is a couple of years old but it should get you started. In Debian, there is documentation about Japanese in Linux http://www.debian.org/doc/devel-manuals#i18n but it is is for developers to get Japanese (and other languages) working correctly in their programs, not for users.
The important trick is remapping your keyboard. I guess that you are having the same problem that I used to have, you don't have a keyboard with 'kanji/kana' keys so you install all the input servers and they run beautifully, no errors, but you just cant tell them that you want to input something! Happy nihongo-linuxing! Eusebio
