Feature/indonesian translation

[Dwixd]

This PR adds Indonesian language support (Bahasa Indonesia) to the application.
Details:

• Added backend/lang/id.json for general translations.
• Created backend/lang/id/ directory containing validation.php and other standard Laravel language files.
• Registered id (Indonesian) locale in the configuration file so it appears in the language selection menu.

Checklist

• I have read the contributing guidelines.
• My code is of good quality and follows the coding standards of the project.
• I have tested my changes, and they work as expected.

[github-actions]

All contributors have signed the CLA ✍️ ✅
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[Dwixd]

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