Feature: Japanese translation

[shamoon]

Proposed change

Big thanks to all translators, especially https://crowdin.com/profile/akama1024

Closes #(issue or discussion)

Type of change

• Bug fix: non-breaking change which fixes an issue.
• New feature / Enhancement: non-breaking change which adds functionality. Please read the important note above.
• Breaking change: fix or feature that would cause existing functionality to not work as expected.
• Documentation only.
• Other. Please explain:

Checklist:

• I have read & agree with the contributing guidelines.
• If applicable, I have included testing coverage for new code in this PR, for backend and / or front-end changes.
• If applicable, I have tested my code for new features & regressions on both mobile & desktop devices, using the latest version of major browsers.
• If applicable, I have checked that all tests pass, see documentation.
• I have run all pre-commit hooks, see documentation.
• I have made corresponding changes to the documentation as needed.
• I have checked my modifications for any breaking changes.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (d165e89) 96.57% compared to head (f1df2fa) 96.57%.
Report is 1 commits behind head on dev.

Additional details and impacted files

@@           Coverage Diff           @@
##              dev    #5641   +/-   ##
=======================================
  Coverage   96.57%   96.57%           
=======================================
  Files         401      401           
  Lines       15845    15847    +2     
  Branches     1226     1226           
=======================================
+ Hits        15303    15305    +2     
  Misses        538      538           
  Partials        4        4           

Flag	Coverage Δ
backend	95.43% <ø> (ø)
frontend	97.94% <100.00%> (+<0.01%)	⬆️

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[github-actions]

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