Most instructions are in Japanese only; only a few puzzles have also English instructions. In the last two weeks I translated ~50 puzzle instructions to English and German, you can find it here: http://www.janko.at/Raetsel/Naoki/
I hope that I will find the time to continue this project; i.e. translate more of Inaba's puzzles. It will be difficult to translate them all, because Inaba probably creates new puzzles faster than I can translate it

Note that I don't speak Japanese and I'm not a natve English speaker too - two sources for mistakes. If you find an error please notify me.
[Not sure whether this fits better to the rules section or the links section in this forum – maybe both.]