Japanese Documentation

What does this MR do and why?

This MR enables Japanese language support on docs.gitlab.com by updating the Hugo configuration to disable English as the default language and enable Japanese localization.

Changes made

• Modified config/_default/hugo.yaml to set disabled: false for the ja-jp language configuration
• Enables Japanese language support on docs.gitlab.com

Launch Plan

Deploy docs.gitlab.com/ja-jp on Wednesday, December 10th at noon PST / 3:00 PM EST / 5:00 AM JST (Dec 11).

1. Site deployment: gitlab-com/localization/docs-site-localization#785 (closed)
2. Monitoring and QA during/post launch: gitlab-com/localization/docs-site-localization#789
3. Blog post announcement: gitlab-com/localization/docs-site-localization#784

Why this change is needed

• Expands GitLab documentation accessibility to Japanese-speaking users
• Supports GitLab's internationalization efforts
• Provides foundation for future Japanese content translation work

Epic for all work related to GTM: gitlab-com/localization#127

Screenshots, screen recordings, or links to review app

How to set up and validate locally

Numbered steps to set up and validate the change are strongly suggested.

1. Configure a local GitLab Docs environment.
2. Check out this branch.
3. Browse the site, in en-us and ja-jp

Merge request acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this merge request.