@i18n-tiny/next

A dependency-free, type-safe, minimal i18n library for Next.js. Simply prepare translation files and call the define function—usable in both Server and Client Components immediately. All key paths such as messages.site.title and t("site.title") are fully typed and auto-suggested, eliminating typos. Static generation features like generateStaticParams can be written cleanly without per-page duplication. Routing, prefixes, and automatic language detection are all handled via a single middleware create() API.

Features

• Type-safe: Full TypeScript support with automatic type inference - autocomplete for messages.site.name, t('common.title'), and all nested keys
• Zero dependencies: No external i18n libraries needed
• Server Components: Native RSC support
• Minimal SSG: Define generateStaticParams once in layout.tsx to statically generate all pages. No per-page configuration needed.
• Simple API: Single configuration, minimal boilerplate
• Small: Minimal bundle size
• No global state: Pure function factory pattern

Installation

npm install @i18n-tiny/next
# or
pnpm add @i18n-tiny/next
# or
yarn add @i18n-tiny/next

Usage

Project Structure

your-app/
├── app/
│   └── [locale]/
│       ├── layout.tsx
│       └── page.tsx
├── messages/
│   ├── en.ts
│   └── ja.ts
├── i18n.ts
└── proxy.ts

Minimal Setup

1. Create message files

Place this file anywhere in your project.

// messages/en.ts
export default {
  common: {
    title: "My Site",
    description: "Welcome to my site"
  },
  nav: {
    home: "Home",
    about: "About"
  }
}

// messages/ja.ts
export default {
  common: {
    title: "マイサイト",
    description: "サイトへようこそ"
  },
  nav: {
    home: "ホーム",
    about: "概要"
  }
}

2. Define i18n instance

Place this file anywhere in your project (i18n.ts, lib/i18n/index.ts, etc.)

// i18n.ts
import { define } from '@i18n-tiny/next'
import { Link } from '@i18n-tiny/next/router'
import enMessages from '@/messages/en'
import jaMessages from '@/messages/ja'

// IMPORTANT: `as const` is required for type inference
export const locales = ['en', 'ja'] as const
export type Locale = (typeof locales)[number]
export const defaultLocale: Locale = 'en'

const { client, server, Provider } = define({
  locales,
  defaultLocale,
  messages: { en: enMessages, ja: jaMessages }
})

export { Link, Provider }
export const { useMessages, useTranslations, useLocale } = client
export const { getMessages, getTranslations } = server

3. Setup Proxy

// proxy.ts (Next.js 16+) or middleware.ts (Next.js 15)
import { create } from '@i18n-tiny/next/proxy'
import { locales, defaultLocale } from '@/i18n'

export const proxy = create({
  locales,
  defaultLocale
})

export const config = {
  matcher: ['/((?!api|_next|.*\\..*).*)*']
}

4. Use in Layout

// app/[locale]/layout.tsx
import { Provider, getMessages, type Locale } from '@/i18n'

export default async function Layout({ children, params }) {
  const { locale } = await params
  const messages = await getMessages(locale)

  return (
    <Provider locale={locale} messages={messages}>
      {children}
    </Provider>
  )
}

5. Use in Components

// Server Component
import { getMessages, getTranslations, type Locale } from '@/i18n'

export async function ServerComponent({ locale }: { locale: Locale }) {
  /* Direct object access */
  const messages = await getMessages(locale)
  /* Function call */
  const t = await getTranslations(locale)

  return (
    <div>
      <h1>{messages.common.title}</h1>
      {/*           ^^^^^ Auto-complete */}
      <p>{t('common.description')}</p>
      {/*    ^^^^^^^^^^^^^^^^^^ Auto-complete */}
    </div>
  )
}

// Client Component
'use client'
import { Link, useMessages, useTranslations } from '@/i18n'

export function ClientComponent() {
  /* Direct object access */
  const messages = useMessages()
  /* Function call */
  const t = useTranslations()

  return (
    <div>
      <h1>{messages.common.title}</h1>
      {/*           ^^^^^ Auto-complete */}
      <Link href="/about">{t('nav.about')}</Link>
      {/*                    ^^^^^^^^^ Auto-complete */}
    </div>
  )
}

That's it! Types are automatically inferred - no manual type annotations needed.

Two ways to access translations:

• messages.common.title - Direct object access (simple and clear)
• t('common.title') - Function call (useful for dynamic keys)

Both are fully typed with autocomplete. Use whichever you prefer!

API Reference

@i18n-tiny/next

define(config)

Defines an i18n instance with automatic type inference.

Parameters:

| Parameter | Type | Description | | --------------- | -------------------------- | ---------------------------------------------------------- | | locales | readonly string[] | Array of supported locales (e.g., ['en', 'ja'] as const) | | defaultLocale | string | Default locale | | messages | Record<Locale, Messages> | Messages object keyed by locale |

Returns:

{
  Provider: React.FC<{ locale: string; messages: Messages; children: ReactNode }>
  locales: readonly string[]
  defaultLocale: string
  server: {
    getMessages: (locale: string) => Promise<Messages>
    getTranslations: (locale: string, namespace?: string) => Promise<TranslationFunction>
  }
  client: {
    useMessages: () => Messages
    useTranslations: (namespace?: string) => TranslationFunction
    useLocale: () => string
  }
}

DefineConfig (type)

Type for the configuration object passed to define().

@i18n-tiny/next/proxy

create(config)

Creates a Next.js proxy (middleware) handler for i18n routing.

Parameters:

| Parameter | Type | Default | Description | | ---------------- | ------------------- | --------------- | ----------------------------------------------------------------------- | | locales | readonly string[] | - | Array of supported locales | | defaultLocale | string | - | Default locale for redirects | | fallbackLocale | string | defaultLocale | Fallback when detection fails | | prefixDefault | boolean | false | Whether to prefix default locale in URLs | | detectLanguage | boolean | true | Whether to detect from Accept-Language | | routing | 'rewrite' | - | SSR rewrite mode (mutually exclusive with prefixDefault/detectLanguage) |

Routing Behavior Matrix:

| prefixDefault | detectLanguage | / behavior | | ------------- | -------------- | ------------------------------------------------ | | false | false | Serves fallbackLocale, no detection | | false | true | Detects, redirects non-default, rewrites default | | true | false | Redirects to /[defaultLocale] | | true | true | Detects and redirects to detected locale |

Examples:

// Default: detect language, redirect non-default, rewrite default
export const proxy = create({
  locales: ['en', 'ja'],
  defaultLocale: 'en'
})

// Always prefix all locales (including default)
export const proxy = create({
  locales: ['en', 'ja'],
  defaultLocale: 'en',
  prefixDefault: true
})

// No detection, always use fallback
export const proxy = create({
  locales: ['en', 'ja'],
  defaultLocale: 'en',
  detectLanguage: false
})

// SSR rewrite mode (locale in x-locale header)
export const proxy = create({
  locales: ['en', 'ja'],
  defaultLocale: 'en',
  routing: 'rewrite'
})

ProxyConfig (type)

Type for the configuration object passed to create().

@i18n-tiny/next/router

Link

Localized Link component that auto-detects locale from current URL.

import { Link } from '@i18n-tiny/next/router'

// Auto-localized (maintains current URL pattern)
<Link href="/about">About</Link>

// Explicit locale override
<Link href="/" locale="ja">日本語</Link>

// Raw path (no localization)
<Link href="/" locale="">English</Link>
<Link href="/" locale={false}>English</Link>

// Conditional locale (false = raw path)
<Link href="/" locale={condition && 'ja'}>Conditional</Link>

@i18n-tiny/core

detectLocale(acceptLanguage, supportedLocales)

Detects the best matching locale from the Accept-Language header.

import { detectLocale } from '@i18n-tiny/core/middleware'

const acceptLanguage = request.headers.get('accept-language')
const locale = detectLocale(acceptLanguage, ['en', 'ja'])
// Returns: 'en' | 'ja' | null

@i18n-tiny/core/router

getLocalizedPath(path, locale, defaultLocale, prefixDefault?)

Generate a localized path with locale prefix.

import { getLocalizedPath } from '@i18n-tiny/core/router'

getLocalizedPath('/about', 'ja', 'en')        // '/ja/about'
getLocalizedPath('/about', 'en', 'en')        // '/about'
getLocalizedPath('/about', 'en', 'en', true)  // '/en/about'

removeLocalePrefix(pathname, locales)

Remove locale prefix from pathname.

import { removeLocalePrefix } from '@i18n-tiny/core/router'

removeLocalePrefix('/ja/about', ['en', 'ja'])  // '/about'
removeLocalePrefix('/ja', ['en', 'ja'])        // '/'
removeLocalePrefix('/about', ['en', 'ja'])     // '/about'

Advanced Usage

Static Site Generation (SSG)

To generate static pages for all locales at build time, add generateStaticParams to your root layout.

// app/[locale]/layout.tsx
import { locales } from '@/i18n'

export function generateStaticParams() {
  return locales.map((locale) => ({ locale }))
}

export default function Layout({ children, params }) {
  // ...
}

Language Switcher

'use client'
import { Link, useLocale } from '@/i18n'

export function LanguageSwitcher() {
  const pathname = usePathname()

  return (
    <div>
      <Link href={pathname} locale="en" normalize> // /ja/about -> /en/about
        English
      </Link>
      <Link href={pathname} locale="ja" normalize> // /en/about -> /ja/about
        日本語
      </Link>
    </div>
  )
}

Examples

See the examples directory for complete working examples.

License

MIT