Internationalization (i18n) Routing

Astro’s internationalization (i18n) features allow you to adapt your project for an international audience. This routing API helps you generate, use, and verify the URLs that your multi-language site produces.

Astro’s i18n routing allows you to bring your multilingual content with support for configuring a default language, computing relative page URLs, and accepting preferred languages provided by your visitor’s browser. You can also specify fallback languages on a per-language basis so that your visitors can always be directed to existing content on your site.

Routing Logic

Astro uses a middleware to implement its routing logic. This middleware function is placed in the first position where it awaits every Response coming from any additional middleware and each page route before finally executing its own logic.

This means that operations (e.g. redirects) from your own middleware and your page logic are run first, your routes are rendered, and then the i18n middleware performs its own actions such as verifying that a localized URL corresponds to a valid route.

You can also choose to add your own i18n logic in addition to or instead of Astro’s i18n middleware, giving you even more control over your routes while still having access to the astro:i18n helper functions.

Configure i18n routing

Both a default language (defaultLocale) and a list of all supported languages (locales) must be specified in an i18n configuration object. Additionally, you can configure more specific routing and fallback behavior to match your desired URLs.

import { defineConfig } from "astro/config"
export default defineConfig({
  i18n: {
    defaultLocale: "en",
    locales: ["es", "en", "pt-br"],
  }
})

Create localized folders

Organize your content folders with localized content by language. Create individual /[locale]/ folders anywhere within src/pages/ and Astro’s file-based routing will create your pages at corresponding URL paths.

Your folder names must match the items in locales exactly. Include a localized folder for your defaultLocale only if you configure prefixDefaultLocale: true to show a localized URL path for your default language (e.g. /en/about/).

Directorysrc
- Directorypages
  - about.astro
  - index.astro
  - Directoryes
    about.astro
    index.astro
  - Directorypt-br
    about.astro
    index.astro

Create links

With i18n routing configured, you can now compute links to pages within your site using the helper functions such as getRelativeLocaleURL() available from the astro:i18n module. These generated links will always provide the correct, localized route and can help you correctly use, or check, URLs on your site.

You can also still write the links manually.

---
import { getRelativeLocaleUrl } from 'astro:i18n';

// defaultLocale is "es"
const aboutURL = getRelativeLocaleUrl("es", "about");
---

<a href="/get-started/">¡Vamos!</a>
<a href={getRelativeLocaleUrl('es', 'blog')}>Blog</a>
<a href={aboutURL}>Acerca</a>

`routing`

Astro’s built-in file-based routing automatically creates URL routes for you based on your file structure within src/pages/.

When you configure i18n routing, information about this file structure (and the corresponding URL paths generated) is available to the i18n helper functions so they can generate, use, and verify the routes in your project. Many of these options can be used together for even more customization and per-language flexibility.

You can even choose to implement your own routing logic manually for even greater control.

`prefixDefaultLocale`

Added in: astro@3.5.0

This routing option defines whether or not your default language’s URLs should use a language prefix (e.g. /en/about/).

All non-default supported languages will use a localized prefix (e.g. /fr/ or /french/) and content files must be located in appropriate folders. This configuration option allows you to specify whether your default language should also follow a localized URL structure.

This setting also determines where the page files for your default language must exist (e.g. src/pages/about/ or src/pages/en/about) as the file structure and URL structure must match for all languages.

"prefixDefaultLocale: false" (default): URLs in your default language will not have a /[locale]/ prefix. All other locales will.
"prefixDefaultLocale: true": All URLs, including your default language, will have a /[locale]/ prefix.

`prefixDefaultLocale: false`

import { defineConfig } from "astro/config"
export default defineConfig({
  i18n: {
    defaultLocale: "en",
    locales: ["es", "en", "fr"],
    routing: {
        prefixDefaultLocale: false
    }
  }
})

This is the default value. Set this option when URLs in your default language will not have a /[locale]/ prefix and files in your default language exist at the root of src/pages/:

Directorysrc
- Directorypages
  - about.astro
  - index.astro
  - Directoryes
    about.astro
    index.astro
  - Directoryfr
    about.astro
    index.astro

src/pages/about.astro will produce the route example.com/about/
src/pages/fr/about.astro will produce the route example.com/fr/about/

`prefixDefaultLocale: true`

import { defineConfig } from "astro/config"
export default defineConfig({
  i18n: {
    defaultLocale: "en",
    locales: ["es", "en", "fr"],
    routing: {
        prefixDefaultLocale: true
    }
  }
})

Set this option when all routes will have their /locale/ prefix in their URL and when all page content files, including those for your defaultLocale, exist in a localized folder:

Directorysrc
- Directorypages
  - index.astro // Note: this file is always required
  - Directoryen
    index.astro
    about.astro
  - Directoryes
    about.astro
    index.astro
  - Directorypt-br
    about.astro
    index.astro

URLs without a locale prefix, (e.g. example.com/about/) will return a 404 (not found) status code unless you specify a fallback strategy.

`redirectToDefaultLocale`

Added in: astro@4.2.0

Configures whether or not the home URL (/) generated by src/pages/index.astro will redirect to /<defaultLocale>.

Setting prefixDefaultLocale: true will also automatically set redirectToDefaultLocale: true in your routing config object. By default, the required src/pages/index.astro file will automatically redirect to the index page of your default locale.

You can opt out of this behavior by setting redirectToDefaultLocale: false. This allows you to have a site home page that exists outside of your configured locale folder structure.

`manual`

Added in: astro@4.6.0

When this option is enabled, Astro will disable its i18n middleware so that you can implement your own custom logic. No other routing options (e.g. prefixDefaultLocale) may be configured with routing: "manual".

You will be responsible for writing your own routing logic, or executing Astro’s i18n middleware manually alongside your own.

import { defineConfig } from "astro/config"
export default defineConfig({
  i18n: {
    defaultLocale: "en",
    locales: ["es", "en", "fr"],
    routing: "manual"
  }
})

Astro provides helper functions for your middleware so you can control your own default routing, exceptions, fallback behavior, error catching, etc: redirectToDefaultLocale(), notFound(), and redirectToFallback():

import { defineMiddleware } from "astro:middleware";
import { redirectToDefaultLocale } from "astro:i18n"; // function available with `manual` routing
export const onRequest = defineMiddleware(async (ctx, next) => {
  if (ctx.url.startsWith("/about")) {
    return next();
  } else {
    return redirectToDefaultLocale(302);
  }
})

middleware function

The middleware function manually creates Astro’s i18n middleware. This allows you to extend Astro’s i18n routing instead of completely replacing it.

You can run middleware with routing options in combination with your own middleware, using the sequence utility to determine the order:

import {defineMiddleware, sequence} from "astro:middleware";
import { middleware } from "astro:i18n"; // Astro's own i18n routing config

export const userMiddleware = defineMiddleware(async (ctx, next) => {
  // this response might come from Astro's i18n middleware, and it might return a 404
  const response = await next();
  // the /about page is an exception and we want to render it
  if (ctx.url.startsWith("/about")) {
    return new Response("About page", {
      status: 200
    });
  } else {
    return response;
  }
});


export const onRequest = sequence(
  userMiddleware,
  middleware({
    redirectToDefaultLocale: false,
    prefixDefaultLocale: true
  })
)

`domains`

Added in: astro@4.9.0

This routing option allows you to customize your domains on a per-language basis for server rendered projects using the @astrojs/node or @astrojs/vercel adapter with a site configured.

Add i18n.domains to map any of your supported locales to custom URLs:

import { defineConfig } from "astro/config"
export default defineConfig({
  site: "https://example.com",
  output: "server", // required, with no prerendered pages
  adapter: node({
    mode: 'standalone',
  }),
  i18n: {
    defaultLocale: "en",
    locales: ["es", "en", "fr", "ja"],
    routing: {
      prefixDefaultLocale: false
    },
    domains: {
        fr: "https://fr.example.com",
        es: "https://example.es"
    }
  }
})

All non-mapped locales will follow your prefixDefaultLocales configuration. However, even if this value is false, page files for your defaultLocale must also exist within a localized folder. For the configuration above, an /en/ folder is required.

With the above configuration:

The file /fr/about.astro will create the URL https://fr.example.com/about.
The file /es/about.astro will create the URL https://example.es/about.
The file /ja/about.astro will create the URL https://example.com/ja/about.
The file /en/about.astro will create the URL https://example.com/about.

The above URLs will also be returned by the getAbsoluteLocaleUrl() and getAbsoluteLocaleUrlList() functions.

`fallback`

Astro’s i18n routing allows you to configure a fallback routing strategy. When a page in one language doesn’t exist (e.g. a page that is not yet translated), instead of displaying a 404 page, you can redirect a user from one locale to another on a per-language basis. This is useful when you do not yet have a page for every route, but you want to still provide some content to your visitors.

For example, the configuration below sets es as the fallback locale for any missing fr routes. This means that a user visiting example.com/fr/my-page/ will be redirected to and shown the content for example.com/es/my-page/ instead of being taken to a 404 page when src/pages/fr/my-page.astro does not exist.

import { defineConfig } from "astro/config"
export default defineConfig({
  i18n: {
    defaultLocale: "en",
    locales: ["es", "en", "fr"],
    fallback: {
      fr: "es"
    }
  }
})

Astro will ensure that a page is built in src/pages/fr for every page that exists in src/pages/es/. If the page does not already exist, then a page with a redirect to the corresponding es route will be created.

Custom locale paths

In addition to defining your site’s supported locales as strings (e.g. “en”, “pt-br”), Astro also allows you to map an arbitrary number of browser-recognized language codes to a custom URL path. While locales can be strings of any format as long as they correspond to your project folder structure, codes must follow the browser’s accepted syntax.

Pass an object to the locales array with a path key to define a custom URL prefix, and codes to indicate the languages mapped to this URL. In this case, your /[locale]/ folder name must match exactly the value of the path and your URLs will be generated using the path value.

This is useful if you support multiple variations of a language (e.g. "fr", "fr-BR", and "fr-CA") and you want to have all these variations mapped under the same URL /fr/, or even customize it entirely (e.g. /french/):

import { defineConfig } from "astro/config"
export default defineConfig({
  i18n: {
    defaultLocale: "en",
    locales: ["es", "en", "fr"],
    locales: ["es", "en", {
        path: "french", // no slashes included
        codes: ["fr", "fr-BR", "fr-CA"]
    }],
    routing: {
        prefixDefaultLocale: true
    }
  }
})

When using functions from the astro:i18n virtual module to compute valid URL paths based on your configuration (e.g. getRelativeLocaleUrl()), use the path as the value for locale.

Limitations

This feature has some restrictions:

The site option is mandatory.
The output option must be set to "server".
There cannot be any individual prerendered pages.
The adapter feature functionPerRoute is not supported.

Astro relies on the following headers in order to support the feature:

X-Forwarded-Host and Host. Astro will use the former, and if not present, will try the latter.
X-Forwarded-Proto and URL#protocol of the server request.

Make sure that your server proxy/hosting platform is able to provide this information. Failing to retrieve these headers will result in a 404 (status code) page.

Browser language detection

Astro’s i18n routing allows you to access two properties for browser language detection in pages rendered on demand: Astro.preferredLocale and Astro.preferredLocaleList. All pages, including static prerendered pages, have access to Astro.currentLocale.

These combine the browser’s Accept-Language header, and your locales (strings or codes) to automatically respect your visitor’s preferred languages.

Astro.preferredLocale: Astro can compute a preferred locale for your visitor if their browser’s preferred locale is included in your locales array. This value is undefined if no such match exists.
Astro.preferredLocaleList: An array of all locales that are both requested by the browser and supported by your website. This produces a list of all compatible languages between your site and your visitor. The value is [] if none of the browser’s requested languages are found in your locales array. If the browser does not specify any preferred languages, then this value will be i18n.locales.
Astro.currentLocale: The locale computed from the current URL, using the syntax specified in your locales configuration. If the URL does not contain a /[locale]/ prefix, then the value will default to i18n.defaultLocale.

In order to successfully match your visitors’ preferences, provide your codes using the same pattern used by the browser.

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