Next.js 16 Internationalization
Complete i18n solution with next-intl or DIY dictionary approach.
Agent Workflow (MANDATORY)
Before ANY implementation, use TeamCreate to spawn 3 agents:
- fuse-ai-pilot:explore-codebase - Analyze existing i18n setup and message files
- fuse-ai-pilot:research-expert - Verify latest next-intl docs via Context7/Exa
- mcp__context7__query-docs - Check locale config and patterns
After implementation, run fuse-ai-pilot:sniper for validation.
Overview
When to Use
- Building multilingual Next.js 16 applications
- Need locale-based routing with
[locale]dynamic segment - Implementing language switcher and URL localization
- Formatting dates, numbers, currencies, and relative times per locale
- SEO optimization with hreflang tags and localized metadata
- Supporting right-to-left (RTL) languages
Why next-intl
| Feature | Benefit |
|---|---|
| App Router native | Full Server Components support |
| Type-safe messages | TypeScript autocompletion for keys |
| ICU MessageFormat | Pluralization, gender, select expressions |
| Async message loading | Load translations on-demand per locale |
| proxy.ts compatible | Works with Next.js 16 proxy pattern |
| Rich formatting | Dates, numbers, lists, relative time |
Two Approaches
1. next-intl (Recommended)
Full-featured library with routing, formatting, and type safety. Best for production applications needing comprehensive i18n support.
2. DIY Dictionary
Lightweight approach using dynamic imports for simple translation needs. Good for projects wanting minimal dependencies.
SOLID Architecture
Module Structure
All i18n code organized in modules/cores/i18n/:
- config/ - Routing configuration, locale definitions
- interfaces/ - TypeScript types for messages and locales
- services/ - Request handlers, message loaders
- messages/ - JSON translation files per locale
File Locations
src/modules/cores/i18n/src/config/routing.ts- Locale routing configsrc/modules/cores/i18n/messages/en.json- English translationssrc/modules/cores/i18n/messages/fr.json- French translationsproxy.ts- Locale detection and redirect logic
Routing Patterns
Locale Segment
All routes prefixed with [locale] dynamic segment:
/en/about→ English about page/fr/about→ French about page/→ Redirects to default locale
Navigation Components
Use localized navigation from next-intl for automatic locale handling:
- Link - Locale-aware anchor links
- redirect - Server-side locale redirect
- usePathname - Current path without locale
- useRouter - Programmatic navigation
Reference Guide
| Need | Reference |
|---|---|
| Initial setup | installation.md, routing-setup.md |
| Route config | routing-config.md, middleware-proxy.md |
| Translations | translations.md, messages-validation.md |
| Formatting | formatting.md |
| Components | server-components.md, client-components.md |
| Navigation | navigation.md |
| TypeScript | typescript.md |
| SEO | seo.md |
| Testing | testing.md |
| DIY approach | diy-dictionaries.md, diy-locale-detection.md |
Message Formatting
ICU MessageFormat
- Pluralization -
{count, plural, one {# item} other {# items}} - Select -
{gender, select, male {He} female {She} other {They}} - Rich text - Support for bold, italic, links in messages
Formatters
- formatDate - Locale-aware date formatting
- formatNumber - Currency, percentages, decimals
- formatList - Conjunction/disjunction lists
- formatRelativeTime - "2 hours ago", "in 3 days"
Best Practices
- Type-safe keys - Use TypeScript for message key autocompletion
- Namespace messages - Organize by feature/page for maintainability
- Server-first - Load translations on server, avoid client bundles
- SEO hreflang - Add alternate links for all locales
- RTL support - Use
dirattribute for right-to-left languages - Fallback locale - Configure default for missing translations
Error Handling
Special Files
Localized error and loading states require specific handling:
[locale]/error.tsx- Localized error boundary[locale]/not-found.tsx- Localized 404 pageglobal-error.tsx- Root error fallback
See error-files.md for complete patterns.