I18N Localization

i18n Localization

Use this skill to plan, review, or harden localization work across product UI, documentation, marketing pages, emails, and web/app routing surfaces.

Canonical Vocabulary

Dispatch

When the user gives no arguments, start with a localization audit of the relevant repository or product surface. Do not ask for locale preferences until the codebase and user request leave a real decision unresolved.

Reference File Index

Critical Rules

1. Treat localization as a product contract, not a translation pass. Cover routing, formatting, accessibility, search metadata, analytics labels, emails, and support surfaces when they are in scope.
2. Never concatenate translated fragments to build a sentence. Use full messages with variables, ICU/select/plural forms, or the framework's equivalent message format.
3. Keep user-visible strings out of business logic and shared constants unless the system already has a catalog abstraction for that layer.
4. Use locale-aware formatters for dates, times, numbers, currencies, lists, relative times, units, and names. Do not hand-roll formatting with string templates.
5. Separate language from region. en, en-US, and en-GB can imply different copy, dates, currency, measurement units, and legal content.
6. Define fallback behavior explicitly. Missing translations should fail visibly in development and degrade intentionally in production.
7. Include pseudo-locale checks for expansion, accenting, bracket markers, interpolation safety, and truncation.
8. Include RTL and bidirectional text checks when any Arabic, Hebrew, Persian, Urdu, or mixed-direction user content can appear.
9. Preserve stable message keys. Do not churn catalogs or invalidate translation memory unless the source message meaning changes.
10. Keep translators away from code syntax. Provide notes, screenshots, variable descriptions, character constraints, and product context.

Workflow

1. Scope The Surface

Identify the surfaces affected by the request:

• UI components, server-rendered pages, native screens, emails, PDFs, docs, notifications, error states, empty states, and transactional copy.
• Route structure, locale negotiation, redirects, canonical URLs, hreflang, sitemap entries, and persisted user locale preferences.
• Data-driven content, CMS fields, markdown/docs content, legal text, pricing, units, and market-specific availability.

If the request is implementation work, read the existing i18n library, routing conventions, catalog format, and test patterns before proposing changes.

2. Extract And Model Messages

For each string-bearing surface:

• Move user-visible strings into the existing catalog or message layer.
• Use full-sentence messages with named variables.
• Model plural, select, gender, ordinal, and count-sensitive text with ICU-style variants or the framework's native equivalent.
• Add translator descriptions for ambiguous labels, product terms, placeholders, and variables.
• Keep stable keys tied to semantic meaning, not English wording alone.

Avoid generic keys such as title, subtitle, or buttonText unless they are nested under a stable feature namespace.

3. Localize Formatting

Check all locale-sensitive values:

• Date, time, timezone, relative time, and calendar assumptions.
• Number, decimal, percent, currency, accounting, compact notation, and unit formatting.
• Lists, names, addresses, phone numbers, postal codes, sorting, casing, and search normalization.
• Form validation, parsing, masks, and server/client round-trip behavior.

Prefer platform formatters such as Intl.*, framework helpers, or vetted library APIs.

4. Route And Persist Locale

Verify:

• How the app chooses a locale: URL prefix, domain, account setting, cookie, browser language, or explicit selector.
• Whether redirects are deterministic and cache-safe.
• Whether canonical URLs, alternate links, metadata, Open Graph, sitemap, robots rules, and docs navigation match the locale strategy.
• Whether APIs, background jobs, and emails receive the same locale context as the visible app.

Do not mix locale negotiation and authentication or billing policy unless the product already couples those concepts.

5. Test And QA

At minimum, recommend or add checks for:

• Catalog completeness and unused key detection.
• Missing interpolation variables.
• Pseudo-locale rendering.
• Snapshot or visual coverage for expanded strings and RTL layout where relevant.
• Formatting tests for representative locales, including at least one non-US locale.
• Accessibility checks for language attributes, direction, screen reader labels, and translated aria text.

For review tasks, report what the available tests prove and what still requires visual or translator QA.

Progressive Disclosure

• Start with this SKILL.md for routing, hard rules, and output shape.
• Read references/localization-checklist.md only when planning, reviewing, or releasing concrete localization work.
• Do not preload unrelated frontend, SEO, copywriting, or JavaScript guidance.
• Use the existing project i18n library and catalog format before introducing new tooling.

Output Shape

Return concise, implementation-oriented output:

• Findings for audits and reviews, ordered by severity with file or route references.
• Plan for implementation requests, ordered by dependency: routing/catalog foundation, extraction, formatting, QA, release.
• Acceptance Criteria that include catalog completeness, pseudo-locale, formatting, fallback, and route/SEO checks when relevant.
• Open Questions only for unresolved choices that cannot be grounded in the codebase or user request.

Do not rewrite marketing copy unless the user explicitly asks for copy editing. Do not perform general frontend redesign unless localization exposes a concrete layout or directionality defect.

Validation Contract

Run from this skill directory before declaring changes complete:

python scripts/check.py

Completion criteria:

1. scripts/check.py exits 0.
2. No portable-CLI violations remain under this skill directory.
3. A smoke review of the dispatch table covers empty, explicit, implicit, and negative-control prompts.