Proxy

Next.js middleware for automatic locale detection and routing.

create(config)

Creates a Next.js Proxy (Middleware) handler for i18n routing.

Parameters:

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

Returns:

• (request: NextRequest) => NextResponse | void: Next.js middleware function.

Routing Behavior Matrix:

prefixDefault	detectLanguage	Behavior at /
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

Example:

// Default: Language detection, non-default redirects, default rewrites
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
})

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

detectLocale(acceptLanguage, supportedLocales)

Detects the best matching locale from the Accept-Language header. Can be imported directly from @i18n-tiny/next/proxy.

Parameters:

Parameter	Type	Required	Description
acceptLanguage	string | null	Required	Value of Accept-Language header
supportedLocales	readonly string[]	Required	Array of supported locales

Returns:

• string | null: The matched locale, or null if no match is found.

Example:

import { detectLocale } from '@i18n-tiny/next/proxy'

const locale = detectLocale(request.headers.get('accept-language'), ['en', 'ja'])