# I18N Handbook

> Internationalization for Next.js App Router - locale routing, message files, and RTL layout checks

- Skill: `bh611627/i18n-handbook` (Agent Skill)
- Install (CLI): `npx skillmds@latest add bh611627/i18n-handbook`
- Raw SKILL.md: https://api.skillmd.com/api/skills/bh611627/i18n-handbook/raw
- Safety review: pending
- Works with: Claude Code, Claude.ai, OpenAI Codex
- Category: Web & Frontend
- Author: bh611627 (https://skillmd.com/u/bh611627)
- Updated: 2026-09-21
- Page: https://skillmd.com/skills/bh611627/i18n-handbook

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# Instructions

## When to Use

- Use for locales, routing, message files, RTL notes.
- Prefer `seo-expert` for hreflang and locale metadata depth.
- Prefer `next-server-patterns` for locale-aware RSC.

Plan **i18n** for **Next.js App Router** without locking to one vendor library unless the repo already uses it.

1. Routing: `[locale]` segment vs subdomain - pros for SEO and DX; pick one.
2. Message catalogs: namespace per feature; avoid mega JSON files.
3. **SEO:** `hreflang` pairs, canonical per locale, localized titles in `metadata`.
4. **RTL:** `dir` on `html` or layout wrapper; mirror spacing where needed.
5. Dates and numbers: `Intl` or established lib - match stack.
## Outcomes

- Locale routing sketch + message file tree + SEO checklist.

## Output Rules

Bullets; no full translation file content unless user provides strings.

## Scope and boundaries

- **In scope:** routing, catalogs, metadata, RTL checklist.
- **Out of scope:** legal translation procurement, TMS integration.

## Safety

- Read-only; do not call paid translation APIs.

## Troubleshooting

- **404 on locale:** middleware matcher and default redirect.
- **Wrong locale flash:** cookie vs accept-language priority documented.

## Related skills

- [`seo-expert`](../seo-expert/SKILL.md) - hreflang and locale metadata
- [`next-server-patterns`](../next-server-patterns/SKILL.md) - locale-aware RSC
- [`markdown-pipeline`](../markdown-pipeline/SKILL.md) - localized MDX

**GitHub:** https://github.com/bh611627/skillcodex/tree/main/skills/i18n-handbook/SKILL.md  
**npm:** https://www.npmjs.com/package/@skillcodex/skills