Update Japanese (ja) translation

[tomoharunagasawa]

We have updated the Japanese translation version. The main updates are as follows.

[2025.6]

• Guide (online): index.ja.md
  • Refined the translation of the text
  • Added the names of the translators
• Guide (PDF): scrum-guide-expansion-pack.ja.pdf
  • Generated the PDF reflecting the changes made to the online guide
• GitHub issue template: translation-error.yml
  • Added Japanese (ja) to the “Translation Community Error Report” issue template

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This change is 

[CLAassistant]

All committers have signed the CLA.

[Copilot]

Pull Request Overview

Updates the Japanese (ja) translation for the Scrum Guide Expansion Pack, including refined text translations, translator credits, and support infrastructure updates.

• Refined Japanese translation text and added translator names to the guide
• Generated updated PDF version reflecting the online guide changes
• Added Japanese language option to the GitHub translation error report template

[tomoharunagasawa]

We plan to update to v2025.6 one more time. If you prefer to update all at once, we will close this pull request.

[tomoharunagasawa]

We have completed the Japanese translation work, including the original text updated in August for v2025.6.

Please review, merge, and publish at your earliest convenience!

[MrHinsh]

@tomoharunagasawa I don't have permission to pull the extra changes across...

[tomoharunagasawa]

@MrHinsh
Sorry, I've changed the settings of japanese repository. Can you access it now?

[MrHinsh]

Im still unable to change it.

[tomoharunagasawa]

@MrHinsh
Still not working?
If syncing the upstream changes here resolves the issue, I'll handle the sync.

[MrHinsh]

@MrHinsh Still not working? If syncing the upstream changes here resolves the issue, I'll handle the sync.

Yea, you just need to sync in the upstream changes

[tomoharunagasawa]

@MrHinsh
Synced it.

[MrHinsh]

Synced it.

Great... I got it on automerge... so once the build uns it should be done.