Update messages_ja_JP.properties

[tkymmm]

Description

Please provide a summary of the changes, including relevant motivation and context.

Closes #(issue_number)

Checklist

• I have read the Contribution Guidelines
• I have performed a self-review of my own code
• I have attached images of the change if it is UI based
• I have commented my code, particularly in hard-to-understand areas
• If my code has heavily changed functionality I have updated relevant docs on Stirling-PDFs doc repo
• My changes generate no new warnings
• I have read the section Add New Translation Tags (for new translation tags only)

[github-actions]

🚀 Translation Verification Summary

🔄 Reference Branch: main-branch

📃 File Check: messages_ja_JP.properties

1. Test Status: ❌ Failed

• Issue:
  • Mismatched line count: 1327 (reference) vs 1317 (current). Comments, empty lines, or translation strings are missing.

2. Test Status: ❌ Failed

• Issue:
  • Missing keys in messages_en_GB.properties: decrypt.serverError, decrypt.invalidPasswordHeader, decrypt.unexpectedError, decrypt.success, decrypt.cancelled, decrypt.invalidPassword, decrypt.passwordPrompt, decrypt.noPassword that are not present in messages_ja_JP.properties.

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❌ Overall Check Status: Failed

@tkymmm please check your translation if it conforms to the standard. Follow the format of messages_en_GB.properties