Middleware

SSR middleware for automatic locale detection and routing.

`create(config)`

Creates an Astro 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
`excludePaths`	`string[]`		`[]`	Paths to exclude from i18n processing
`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:

MiddlewareHandler: Astro middleware handler.

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 onRequest = defineMiddleware(
  create({
    locales: ['en', 'ja'],
    defaultLocale: 'en'
  })
)

// SSR rewrite mode (locale in Astro.locals)
export const onRequest = defineMiddleware(
  create({
    locales: ['en', 'ja'],
    defaultLocale: 'en',
    routing: 'rewrite'
  })
)

SSR Rewrite Mode

When using routing: 'rewrite', the locale is stored in Astro.locals.locale.

---
// src/pages/index.astro (No [locale] folder needed)
import { getMessages } from '../i18n'

const locale = Astro.locals.locale  // 'en' or 'ja'
const messages = getMessages(locale)
---

<html lang={locale}>
  <body>
    <h1>{messages.common.title}</h1>
  </body>
</html>

`detectLocale(acceptLanguage, supportedLocales)`

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

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.

create(config)​

SSR Rewrite Mode​

detectLocale(acceptLanguage, supportedLocales)​

`create(config)`

SSR Rewrite Mode

`detectLocale(acceptLanguage, supportedLocales)`