WIP: Fix some errors in the Japanese translation added in 9.4

Description

After having merged the Japanese translation to master (!12693 (merged), !12826 (merged)), some errors that weren't easy to spot on Zanata became obvious when we started to use the translated UI.

This MR will serve as a hub to collect translation suggestions and debate those improvements. Feel free to start a discussion on any line of translation you'd like to be fixed.

This is a internationalization Community Contribution MR.

Currently a WIP as to have enough time to spot other errors and end every ensuing discussion.

cc @Tetya, @tnir, @jeffi7, @tetsukay, @masakura, @dosuken123

ping @htve

Note: the translation efforts are currently coordinated in #32951 (closed)