I installed ibus-anthy slackbuild, i can see japanese input and it work as user login.
You are right, it might be an access rights problem.
I have tested ibus-tables using src2pkg.
Those ibus-tables I installed are
ibus-table-1.3.0 (root-ok) (user-no)
ibus-table-1.3.9 (root-ok) (user-no)
ibus-table-1.4.99 (root-ok) (user-no)
ibus-table-1.5.0 (did not work at all)
you haven't configured methods for this particular user.
BTW, do I need configure methods for particular user. I don't know that.
How to do that.
I think, that is solution.