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I18n

Skill Syo-M/fable-frontend-skills/.claude/skills/i18n

Internationalization and localization — message catalogs, ICU plurals/interpolation, Intl formatting, locale routing, RTL, locale-aware input validation. Use when adding or fixing translations, multi-locale UI, date/number/currency formatting, language switching, or RTL support. 日本語の依頼例:「多言語対応」「i18n入れて」「翻訳」「ロケール切り替え」「日付/通貨の表示」「RTL対応」「言語切替」。From its SKILL.md

Install
npx -y skills add Syo-M/fable-frontend-skills --skill i18n

Assembled from the repository path, not quoted from the project. Check it against their README if it does not work.

One thing to look at

  • 3 stars3 stars. Stars are a popularity signal and not a quality one, but at this level it is likely that nobody has read this closely except its author, and you would be relying on your own review.

SKILL.md

4.2 KB, 891 tokens by cl100k_base, as published. Nobody here has run it

Internationalization

No hardcoded user-facing strings

  • Every user-visible string comes from a message catalog keyed by ID — never a literal in JSX. This is the one rule that, if skipped, makes everything else impossible to retrofit.
  • Use the framework-idiomatic library: next-intl (Next.js App Router), react-i18next / react-intl (Vite SPA), Astro's i18n routing + a catalog. One per repo (dependency ask-first rule applies).
  • Keys are semantic and namespaced (checkout.payment.submit), not the English text. Keep catalogs shallow (≤3 levels) and run a missing/orphaned-key check in CI (i18next-parser --fail-on-update, or the library's extractor) — wire it as a gate, don't rely on memory.
  • Translator-facing context: provide a description for ambiguous keys; never concatenate sentence fragments across keys (word order differs per language).

Plurals, gender, interpolation — ICU MessageFormat

  • Never build plurals with count === 1 ? 'item' : 'items' — many languages have 3–6 plural categories. Use ICU {count, plural, ...} and let the library + locale data decide.
  • Interpolate variables through the catalog ({name}), never via template-string concatenation around a translated fragment.
  • Rich/linked text: use the library's component interpolation (<Trans> / t.rich), not dangerouslySetInnerHTML on a translated string (see frontend-security).

Formatting — always Intl, never hand-rolled

  • Dates/times: Intl.DateTimeFormat with an explicit locale and time zone. Store/transport UTC; render in a deliberately chosen zone; label it when ambiguous (consistent with data-viz).
  • Numbers/currency/units/lists: Intl.NumberFormat (with style: 'currency' + currency code), Intl.ListFormat, Intl.RelativeTimeFormat. No manual thousands separators, decimal marks, or "3 days ago" strings — these differ per locale.
  • Currency: format with the data's currency, not the UI locale's; never assume $.

Routing & locale negotiation

  • Locale in the URL (/ja/... subpath, or domain) so pages are linkable, cacheable, and indexable — not only a cookie/header. Emit hreflang alternates and set <html lang> (and dir) per request.
  • Negotiate initial locale from the URL → stored preference → Accept-Language, with a sane default; let users switch explicitly and persist it.
  • SSR/RSC: load only the active locale's catalog on the server and pass it down; don't ship every language's messages to the client (bundle bloat). Code-split catalogs by locale/route.

RTL & layout

  • Drive direction from data: <html dir="rtl"> for RTL locales; never hardcode LTR assumptions.
  • Use CSS logical properties (margin-inline, inset-inline-start, text-align: start) — mandated already by css-modules, and the reason it's mandated. Physical left/right breaks RTL.
  • Mirror directional icons (arrows, chevrons) in RTL; don't mirror logos or media. Test one RTL locale (e.g. ar) as a first-class case, plus a pseudo-locale for length/encoding.

Locale-aware input & validation

  • Accept locale-formatted input (decimal comma, native digits, local date order) and parse to a canonical form before validating with zod (see frontend-security) — validate the parsed value, store canonical.
  • Names/addresses/phone: don't assume Western structure (first/last, state/ZIP). Keep fields permissive; avoid regex that rejects valid non-Latin input.
  • Sorting/search: locale-aware collation (Intl.Collator), not byte order.

Testing

  • Pseudo-localization (accented + padded strings) in a story/build catches truncation, clipping, and hardcoded strings early (pairs with visual-regression over both LTR and one RTL locale).
  • Stories cover at least one non-English and one RTL locale for layout-sensitive components (see storybook).

What ships with it

Read from the repository

Just SKILL.md. No reference files, no scripts.

Gives 2 of the 12 instructions most translation skills give in 891 tokens

Counted across 286 of the 304 authors here whose files we hold, read 2026-09-06

  • Preserve all markdown formattingin 8 of 286, across 5 files
  • Use ICU message format for complex stringshere, and in 8 of 286
  • Preserve all numbers, dates, and amounts exactlyin 7 of 286
  • Use CSS logical properties for RTL layoutsin 7 of 286
  • Format dates, numbers, and currencies with FormatStylehere, and in 7 of 286, across 6 files
  • Use locale-aware formatters for dates, numbers, and currencyin 7 of 286
  • Merge translated chunks in orderin 6 of 286, across 3 files
  • Use logical CSS properties instead of physical onesin 6 of 286
  • Use leading and trailing, never left and rightin 6 of 286, across 5 files
  • Use time-limited SAS URLs for document translationin 5 of 286, across 2 files
  • Split long content at markdown block boundariesin 5 of 286, across 2 files
  • Run first-time setup before any translation when preferences missingin 5 of 286, across 2 files

Said here and by no other author read

  • Use the framework-idiomatic i18n library
  • Key catalogs semantically and namespaced, not English text
  • Run missing-key checks in CI as a gate
  • Store UTC; render in an explicit time zone
  • Put the locale in the URL
  • Load only the active locale's catalog on the server

Grouped from the skills themselves: near-identical wordings counted once, and counted by distinct author, so one author publishing three of these counts once. Length counted with cl100k_base; the agent that loads this file may tokenize it differently.

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