[WWW5911]

Pull Request

Description

Add Traditional Chinese (zh-TW) as a supported console locale.

• Add i18n/locales/zh-TW.json, aligned 1:1 with en-US.json (2315 keys, same order, all {placeholders} preserved, Taiwan terminology).
• Register zh-TW in LOCALE_FILE_MAP. zh-TW, zh_TW, zh-Hant, zh-Hant-TW, zh-HK, zh-MO resolve to it. zh, zh-CN, zh-Hans, zh-SG still resolve to Simplified Chinese.
• Switch the i18next load option from "languageOnly" to "currentOnly". With languageOnly, i18next collapses zh-TW to zh and always serves Simplified Chinese. All other locale codes are already language-only, so they are unaffected.
• Language switcher: label the existing option 簡體中文 and add 繁體中文. Resolve the current locale with normalizeLocale() instead of split("-")[0].
• Date picker: use the date-fns zhTW locale for zh-TW.
• README: list Traditional Chinese among the supported languages.

Type of Change

• New feature (non-breaking change which adds functionality)

Testing

• Unit tests added/updated
• Manual testing completed

New tests:

• tests/lib/i18n-config.test.js: Traditional Chinese variants resolve to zh-TW, Simplified variants stay on zh, and getLocaleFile("zh-TW") returns zh-TW.
• tests/lib/datetime-picker.test.js: zh-TW maps to the date-fns zh-TW locale.

Run on Node 22 and pnpm 12.3.4 in an LF checkout (same as CI):

pnpm install --frozen-lockfile   # ok
pnpm type-check                  # ok
pnpm lint                        # ok
pnpm format:check                # ok
pnpm test:run                    # 869 passed, 0 failed

Checklist

• Code follows the project's style guidelines
• Self-review completed
• TypeScript types are properly defined
• All commit messages are in English (Conventional Commits)
• All existing tests pass
• No new dependencies added, or they are justified

Related Issues

Closes #

Screenshots (if applicable)

Before	After

Additional Notes

• UI text change: the existing 中文 option is renamed to 簡體中文 so the two Chinese options can be told apart. Please confirm this is acceptable under the migration rule on page text changes.
• zh-HK / zh-MO → zh-TW is a judgment call (closer script than Simplified Chinese). Easy to drop if not wanted.