i18n Expert

name: i18n-expert
description: This skill should be used when setting up, auditing, or enforcing internationalization/localization in UI codebases (React/TS, i18next or similar, JSON locales), including installing/configuring the i18n framework, replacing hard-coded strings, ensuring en-US/zh-CN coverage, mapping error codes to localized messages, and validating key parity, pluralization, and formatting.

I18n Expert

Overview

Deliver a complete i18n setup + audit pass: configure the i18n framework, replace user-facing strings with keys, ensure locale parity, and validate pluralization/formatting for en-US and zh-CN.

Core Capabilities

• Library selection and setup (React, Next.js, Vue).
• Key architecture and locale file organization.
• Translation generation and quality strategy (AI, professional, manual).
• Routing and language detection/switching.
• SEO and metadata localization (when applicable).
• RTL support (only if RTL locales are in scope).

Scope Inputs (ask if unclear)

• Framework and routing style.
• Existing i18n state (none, partial, legacy).
• Target locales (default: en-US + zh-CN).
• Translation quality needs (AI vs professional vs manual).
• Locale formats in use (JSON, YAML, PO, XLIFF).
• Formality/cultural requirements (if any).

Workflow (Audit -> Fix -> Validate)

1. Confirm scope and locale targets

• Identify the i18n framework and locale locations.
• Confirm locales; default to en-US + zh-CN when specified.

2. Setup i18n baseline (if missing)

• Choose a framework-appropriate library (e.g., React: react-i18next; Next.js: next-intl; Vue: vue-i18n).
• Install packages and create the i18n entry/config file.
• Wire the provider at the app root and load locale resources.
• Add a language switcher and persistence (route/param/localStorage) as appropriate.
• Establish locale file layout and key namespaces.
• If routing is locale-aware, define the locale segment strategy early (subpath, subdomain, query param).
• If metadata is user-facing, include translation for titles/descriptions.

3. Audit key usage and locale parity

• Run:

  python scripts/i18n_audit.py --src <src-root> --locale <path/to/en-US.json> --locale <path/to/zh-CN.json>
  

• Treat missing keys/parity gaps as blockers.
• Manually verify dynamic keys (t(var)).

4. Find raw user-facing strings

• Search:

  rg -n --glob '<src>/**/*.{ts,tsx,js,jsx}' "<[^>]+>[^<{]*[A-Za-z][^<{]*<"
  rg -n --glob '<src>/**/*.{ts,tsx,js,jsx}' "aria-label=\"[^\"]+\"|title=\"[^\"]+\"|placeholder=\"[^\"]+\""
  

• Localize accessibility labels.

5. Replace strings with keys

• Use t('namespace.key') for UI text.
• For plurals use t('key', { count }) + _one/_other keys.
• Use Intl/app formatters for time/date/number.

6. Localize error handling (critical)

• Map error codes to localized keys; show localized UI only.
• Log raw error details only.
• Provide localized fallback for unknown codes.

7. Update locale files

• Add missing keys in both locales.
• Keep placeholders consistent; avoid renames unless requested.
• Generate translations using the agreed method; preserve placeholders and plural rules.

8. Validate

• Re-run the audit until missing/parity issues are zero.
• Validate JSON (e.g., python -m json.tool <file>).
• Update tests asserting visible text.

Guardrails

• Never expose raw error.message to UI; show localized strings only.
• Do not add extra locales unless explicitly requested.
• Prefer structured namespaces (e.g., errors.*, buttons.*, workspace.*).
• Keep translations concise and consistent.
• Some technical/brand terms should remain untranslated (e.g., product name, API, MCP, Bash).

Deliverables (expected outputs)

• i18n config/provider wiring.
• Locale files for each target language.
• Replaced UI strings with stable keys.
• Language switcher and persistence (if applicable).
• Updated tests for visible text.

Architecture Guidance (keep concise)

• Key structure: prefer nested namespaces by area (e.g., common.buttons.save, pricing.tier.pro).
• File layout: one file per locale or per-locale namespaces; keep keys in sync across locales.
• Placeholders: preserve {name}/{{name}} exactly; validate plurals by locale rules.
• Formatting: use Intl/app helpers for date, time, number, and list formatting.
• SEO/metadata: localize titles and descriptions if the app exposes them.
• RTL: only needed for RTL locales; use logical CSS properties and test layout.
• Non-web surfaces (Electron main-process dialogs, CLI prompts, native menus) need localization too.

Performance Notes (short)

• Lazy-load locale bundles when the app supports it.
• Split large locale files by namespace.

Failure Modes (watchlist)

• Missing translations: fall back to default locale and log warnings.
• RTL layout issues: verify logical CSS and test pages.
• SEO missing: ensure alternates and metadata are localized when applicable.

Validation Checklist (short)

• No missing keys and no raw UI strings.
• Locale switching works and persists.
• Plurals and formatting verified in both locales.
• Fallback locale configured.

Resources

scripts/

• scripts/i18n_audit.py: Extracts t('key') usage and compares against locale JSON files.