Add japanese language support

[Tt0x]

What changes I've made

I would like to contribute Japanese language support to Hi.Events. I have added Japanese translations (with the help of Claude Sonnet 5.5) and the necessary locale configuration, including date formatting. I had native speakers check the translation.

Why I've made these changes

It will be a very helpful contribution to the Japanese community!

How I've tested these changes

I ran it and had it checked. The only thing I could not resolve is the Language Menu. There is still "ja" written instead of 'Japanese' or '日本語'.

Thank you for Hi.Events!

Checklist

• I have read the contributing guidelines.
• My code follows the coding standards of the project.
• I have tested my changes, and they work as expected.
• I understand that this PR will be closed if I do not follow the contributor guidelines and if this PR template is left unedited.

[github-actions]

All contributors have signed the CLA ✍️ ✅
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[Tt0x]

I have read the CLA Document and I hereby sign the CLA

[daveearley]

Thank you very much for this, @Tt0x . Very much appreciated.