PR: Update translation jp

[sohnishi]

I'm very sorry for missing @ccordoba12 's announce #3430 about translations.
I updated the Japanese translation for current version.
Please accept my apology and update files.

Or I wonder I should wait for the next major release.

[ccordoba12]

@sohnishi, thanks a lot for updating the Japanese translations! However, we need you to redo this pull request against the 3.x branch (instead of master) so we can merge it for 3.1.

For that you need to follow these steps:

1. git checkout 3.x (to place yourself in 3.x branch of your fork).
2. git checkout -b jp_update_1 (to create a branch for you to update the translations)
3. Move the files in this pull request to that branch
4. Commit and push again to Github.
5. Create a new pull request with your changes.

Thanks for your help :-)

[sohnishi]

Thank you. I will try this backport work soon.

[ccordoba12]

Thanks @sohnishi! Closing this one for now then :-)