Internationalized Routing

Blitz has built-in support for internationalized (i18n) routing. You can provide a list of locales, the default locale, and domain-specific locales and Blitz will automatically handle the routing.

The i18n routing support is currently meant to complement existing i18n library solutions like react-intl, react-i18next, lingui, rosetta, and others by streamlining the routes and locale parsing.

Getting started

To get started, add the i18n config to your blitz.config.js file.

Locales are UTS Locale Identifiers, a standardized format for defining locales.

Generally a Locale Identifier is made up of a language, region, and script separated by a dash: language-region-script. The region and script are optional. An example:

en-US - English as spoken in the United States
nl-NL - Dutch as spoken in the Netherlands
nl - Dutch, no specific region

// blitz.config.js
module.exports = {
  i18n: {
    // These are all the locales you want to support in
    // your application
    locales: ["en-US", "fr", "nl-NL"],
    // This is the default locale you want to be used when visiting
    // a non-locale prefixed path e.g. `/hello`
    defaultLocale: "en-US",
    // This is a list of locale domains and the default locale they
    // should handle (these are only required when setting up domain routing)
    domains: [
      {
        domain: "example.com",
        defaultLocale: "en-US",
      },
      {
        domain: "example.nl",
        defaultLocale: "nl-NL",
      },
      {
        domain: "example.fr",
        defaultLocale: "fr",
      },
    ],
  },
}

Locale Strategies

There are two locale handling strategies: Sub-path Routing and Domain Routing.

Sub-path Routing

Sub-path Routing puts the locale in the url path.

// blitz.config.js
module.exports = {
  i18n: {
    locales: ["en-US", "fr", "nl-NL"],
    defaultLocale: "en-US",
  },
}

With the above configuration en-US, fr, and nl-NL will be available to be routed to, and en-US is the default locale. If you have a pages/blog.js the following urls would be available:

/blog
/fr/blog
/nl-nl/blog

The default locale does not have a prefix.

Domain Routing

By using domain routing you can configure locales to be served from different domains:

// blitz.config.js
module.exports = {
  i18n: {
    locales: ["en-US", "fr", "nl-NL", "nl-BE"],
    defaultLocale: "en-US",

    domains: [
      {
        domain: "example.com",
        defaultLocale: "en-US",
      },
      {
        domain: "example.fr",
        defaultLocale: "fr",
      },
      {
        domain: "example.nl",
        defaultLocale: "nl-NL",
        // specify other locales that should be redirected
        // to this domain
        locales: ["nl-BE"],
      },
    ],
  },
}

For example if you have pages/blog.js the following urls will be available:

example.com/blog
example.fr/blog
example.nl/blog
example.nl/nl-BE/blog

Automatic Locale Detection

When a user visits the application root (generally /), Blitz will try to automatically detect which locale the user prefers based on the Accept-Language header and the current domain.

If a locale other than the default locale is detected, the user will be redirected to either:

When using Sub-path Routing: The locale prefixed path
When using Domain Routing: The domain with that locale specified as the default

When using Domain Routing, if a user with the Accept-Language header fr;q=0.9 visits example.com, they will be redirected to example.fr since that domain handles the fr locale by default.

When using Sub-path Routing, the user would be redirected to /fr.

Disabling Automatic Locale Detection

The automatic locale detection can be disabled with:

// blitz.config.js
module.exports = {
  i18n: {
    localeDetection: false,
  },
}

When localeDetection is set to false Blitz will no longer automatically redirect based on the user's preferred locale and will only provide locale information detected from either the locale based domain or locale path as described above.

Accessing the locale information

You can access the locale information via the Blitz router. For example, using the useRouter() hook the following properties are available:

locale contains the currently active locale.
locales contains all configured locales.
defaultLocale contains the configured default locale.

When pre-rendering pages with getStaticProps or getServerSideProps, the locale information is provided in the context provided to the function.

When leveraging getStaticPaths, the configured locales are provided in the context parameter of the function under locales and the configured defaultLocale under defaultLocale.

Transition between locales

You can use Link or Router to transition between locales.

For Link, a locale prop can be provided to transition to a different locale from the currently active one. If no locale prop is provided, the currently active locale is used during client-transitions. For example:

import {Link} from "blitz"

export default function IndexPage(props) {
  return (
    <Link href="/another" locale="fr">
      <a>To /fr/another</a>
    </Link>
  )
}

When using the Router methods directly, you can specify the locale that should be used via the transition options. For example:

import {useRouter} from "blitz"

export default function IndexPage(props) {
  const router = useRouter()

  return (
    <div
      onClick={() => {
        router.push("/another", "/another", {locale: "fr"})
      }}
    >
      to /fr/another
    </div>
  )
}

If you have a href that already includes the locale you can opt-out of automatically handling the locale prefixing:

import {Link} from "blitz"

export default function IndexPage(props) {
  return (
    <Link href="/fr/another" locale={false}>
      <a>To /fr/another</a>
    </Link>
  )
}

Blitz supports overriding the accept-language header with a NEXT_LOCALE=the-locale cookie. This cookie can be set using a language switcher and then when a user comes back to the site it will leverage the locale specified in the cookie.

For example, if a user prefers the locale fr but a NEXT_LOCALE=en cookie is set the en locale will be used instead until the cookie is removed or expired.

Search Engine Optimization

Since Blitz knows what language the user is visiting it will automatically add the lang attribute to the <html> tag.

Blitz doesn't know about variants of a page so it's up to you to add the hreflang meta tags using Head. You can learn more about hreflang in the Google Webmasters documentation.

How does this work with Static Generation?

Automatically Statically Optimized Pages

For pages that are automatically statically optimized, a version of the page will be generated for each locale.

Non-dynamic getStaticProps Pages

For non-dynamic getStaticProps pages, a version is generated for each locale like above. getStaticProps is called with each locale that is being rendered. If you would like to opt-out of a certain locale from being pre-rendered, you can return notFound: true from getStaticProps and this variant of the page will not be generated.

export async function getStaticProps({locale}) {
  // Call an external API endpoint to get posts.
  // You can use any data fetching library
  const res = await fetch(`https://.../posts?locale=${locale}`)
  const posts = await res.json()

  if (posts.length === 0) {
    return {
      notFound: true,
    }
  }

  // By returning { props: posts }, the Blog component
  // will receive `posts` as a prop at build time
  return {
    props: {
      posts,
    },
  }
}

Dynamic getStaticProps Pages

For dynamic getStaticProps pages, any locale variants of the page that is desired to be prerendered needs to be returned from getStaticPaths. Along with the params object that can be returned for the paths, you can also return a locale field specifying which locale you want to render. For example:

// pages/blog/[slug].js
export const getStaticPaths = ({locales}) => {
  return {
    paths: [
      {params: {slug: "post-1"}, locale: "en-US"},
      {params: {slug: "post-1"}, locale: "fr"},
    ],
    fallback: true,
  }
}