It seems that Japanese Translation activities are not that active. So, I put the po for Japanese here.
KDE JP suggests peculiar use of po for plurals for Japanese (keeping nplurals=2 even though Japanese has no plurals):
It's against the standard practice of gettext, and it has no sense for Kleo at all, so, I don't follow that (follow the standard practice, instead).
I assume that it's OK for the upstream to push the translation.