Japanese translation files

[keichan34]

Summary of changes

Adds Japanese translation files.

Checklist

• New functions have typespecs, changed functions were updated
• Same for documentation, including moduledocs
• Tests were added or updated to cover changes
• Commits were squashed into a single coherent commit

[coveralls]

Coverage increased (+0.04%) to 70.741% when pulling 4f9f913 on keichan34:japanese into fcacaff on bitwalker:master.

[bitwalker]

@keichan34 Is this ready for merge? I assume so, just want to make sure you weren't still working on it before I merge it.

[keichan34]

@bitwalker Ah yes, it's ready.

[bitwalker]

Thanks so much!