[chore](i18n) Remove Japanese docs and the EN->JA translation pipeline

[morningman]

Versions

• dev
• 4.x
• 3.x
• 2.1 or older (not covered by version/language sync gate)

(Applies to all versions: the Japanese tree carried current / 4.x / 3.x / 2.1 copies.)

Languages

• Chinese
• English

Japanese only — Chinese and English content are untouched.

What this does

Removes the Japanese locale from the website entirely, together with the pipeline that produced it.

Deleted

• ja-source/ — 5,703 files, the Japanese doc source tree
• ja-build/ — the prebuilt Japanese site copied into build/ja at deploy time
• scripts/i18n/ — all 9 scripts. Every one was added by the original feat(website): i18n ja (#3468) commit, and nothing outside the translation workflow referenced them.
• .github/workflows/manual-i18n-translate-workflow.yaml — the EN→JA translation pipeline

Deploy workflows

cron-deploy-website.yml and manual-deploy-website.yml no longer guard on ja-build or copy it into build/ja. Their build step already passed only --locale en --locale zh-CN, so nothing else about the build changed.

Site config

• docusaurus.config.js: locales → ['en', 'zh-CN']; dropped the ja localeConfig, the /ja/search sitemap exclusion, 'ja' from the search languages, and the ja/docs / ja/course route bases
• config/custom-docusaurus-plugin.js, scripts/update_search_hash.js, and the start:ja / write-translations:ja package scripts
• src/theme/TOC/index.tsx: dropped the Japanese UI-string branch
• scripts/patch-search-tokenize.js: removed the two Japanese-only node_modules patches (kana tokenizer preference, zh+ja mixed-mode tokenizer). The four locale-aware search patches stay — zh-CN still needs them.

Docs governance

The ja locale, the ja_source content root, and the i18n-sync-locale-candidate rule are removed from .docs-governance/rules.yml, manifest.js, lint-links.js, lint-seo.js, and lint-i18n-sync.js, with matching test updates. i18n-sync-policy.md, translation-glossary.yml, the exceptions.yml example, and the PR template's Japanese checkbox are updated to match.

website-quality-governance/broken-links-baseline.md: the ja-source/ rows are dropped and its 502 internal errors subtracted from the internal tables (exact per-root counts from the same scan). The external info count has no per-root breakdown and still reflects the original scan; the file now says so.

Notes for reviewers

Two deliberate judgment calls:

• The locale dropdown's "Coming Soon" badge is kept. ja was its only member, so COMING_SOON_LOCALES is now an empty set; the markup and styles are untouched so a future locale can use it.
• src/utils/tokenize.ts is left alone. Its ["ja", "jp", "th"] list is a vendored copy of the upstream search-plugin util (added well before the Japanese work), and jp / th are equally unused there. Removing just ja would be arbitrary.

Docs Checklist

• Checked by AI
• Test Cases Built
• Updated required version and language counterparts, or explained why not
• If only one language changed, confirmed whether source/translation counterparts need sync

yarn docs-governance:test passes 37/37. No site build was run locally.

🤖 Generated with Claude Code