fix(i18n): synchronize locale plural forms

[VailElla]

Description

Keep every shipped locale synchronized with i18next plural extraction and runtime resolution. Generated empty plural variants could force a counted label to fall through to another language; this PR gives every generated variant a non-empty same-locale value and verifies the exact runtime plural key used for each locale.

Type of Change

• Bug fix
• New feature
• Breaking change
• Performance improvement
• Code refactoring
• Documentation update
• UI/UX improvement
• Build/CI or Dependency update

Changes Made

• Include the already shipped Korean locale in the i18next CLI locale set.
• Synchronize generated plural variants across all shipped locales.
• Populate generated variants with non-empty same-locale text; where no dedicated grammatical form already existed, reuse the locale's existing generic or base phrasing.
• Set returnEmptyString: false as a defensive runtime fallback.
• Add scripts/check-i18n-runtime.mjs and run it from npm run i18n:check; it rejects empty translations, cross-language fallback, and resolution to the wrong plural suffix.

Screenshots/Videos

Not applicable; this fixes localization resolution rather than layout.

Testing

• I have tested these changes locally and confirmed that they work as expected without issues

• npm run i18n:check — passed with no generated-file drift and 952 exact plural resolutions across all 12 shipped locales.

• Runtime validation covers every Intl.PluralRules category available to each locale and requires the requested locale, expected suffixed key, and a non-empty result.

• npm run build — passed; only the existing large-chunk warning remains.

• npm run typecheck — matches current main at 117 existing diagnostics.

• npm run i18n:lint — matches current main at 36 existing hardcoded-string findings.

• npx eslint scripts/check-i18n-runtime.mjs — passed.

• Changed-file Prettier check — passed.

• git diff --check origin/main...HEAD — passed.

• Revalidated on 2026-07-18 against upstream main at 026a78f7: branch head 0617b400 matches the PR head; production build, diff check, runtime i18n validation, targeted ESLint, and Prettier passed; typecheck remains equal to the 117-diagnostic main baseline.

Test Configuration:

• OS: macOS 26.5.2
• Hardware: Apple M4 Pro (arm64)

Checklist

• My code follows the project's code style
• I haven't added unnecessary AI-generated code comments
• My changes generate no new warnings or errors

Additional Notes

This PR should land before #1370. The two PRs overlap mechanically in i18next.config.ts and locale JSON files but have no behavioral dependency; #1370 should rebase after this PR merges.

AI Disclaimer:

• This PR is entirely AI-generated
• This PR is AI-generated but guided by a human
• This PR was handwritten with AI assistance (spell check, logic suggestions, error resolving)
• This PR contains only blood, sweat, and coffee (AI-free)

[CyberTimon]

Excellent PR! Is it possible to move the script into src/i18n to not bloat the root directory with folders?

[CyberTimon]

Amazing, thanks so much for the quick fix! LGTM

[VailElla]

Thank you! Glad the updated placement works, and I really appreciate the quick review and merge.