Domain routing for locales in NextJS

Introduction

Domain routing for locales lets your website show different languages or content based on the website address people use. It helps visitors see the right version automatically.

You want visitors from different countries to see your site in their language automatically.

You have multiple websites with different domain names for each language or region.

You want to improve user experience by showing local content based on the domain.

You want to manage language versions without changing the URL path.

You want search engines to recognize different domains for different languages.

Syntax

NextJS

module.exports = {
  i18n: {
    locales: ['en', 'fr', 'de'],
    defaultLocale: 'en',
    domains: [
      {
        domain: 'example.com',
        defaultLocale: 'en'
      },
      {
        domain: 'example.fr',
        defaultLocale: 'fr'
      },
      {
        domain: 'example.de',
        defaultLocale: 'de'
      }
    ]
  }
};

This code goes inside next.config.js to tell Next.js about your locales and domains.

The domains array links each domain to a default language.

Examples

This example sets up English and Spanish with two domains.

NextJS

module.exports = {
  i18n: {
    locales: ['en', 'es'],
    defaultLocale: 'en',
    domains: [
      { domain: 'mysite.com', defaultLocale: 'en' },
      { domain: 'mysite.es', defaultLocale: 'es' }
    ]
  }
};

This example uses English and Japanese with separate domains.

NextJS

module.exports = {
  i18n: {
    locales: ['en', 'ja'],
    defaultLocale: 'en',
    domains: [
      { domain: 'example.com', defaultLocale: 'en' },
      { domain: 'example.jp', defaultLocale: 'ja' }
    ]
  }
};

Sample Program

This example configures two domains for English and French. The page shows a greeting based on the current locale detected from the domain.

NextJS

/* next.config.js */
module.exports = {
  i18n: {
    locales: ['en', 'fr'],
    defaultLocale: 'en',
    domains: [
      { domain: 'myapp.com', defaultLocale: 'en' },
      { domain: 'myapp.fr', defaultLocale: 'fr' }
    ]
  }
};

/* pages/index.js */
import { useRouter } from 'next/router';

export default function Home() {
  const { locale } = useRouter();
  return (
    <main>
      <h1>{locale === 'fr' ? 'Bonjour!' : 'Hello!'}</h1>
      <p>{locale === 'fr' ? 'Bienvenue sur notre site.' : 'Welcome to our site.'}</p>
    </main>
  );
}

Important Notes

Make sure your DNS and hosting are set up to point each domain to your Next.js app.

Next.js automatically detects the locale from the domain and serves the right content.

You can add more domains and locales by extending the domains array.

Summary

Domain routing lets you serve different languages on different website addresses.

Configure domains and locales in next.config.js under the i18n key.

Your app can show content based on the detected locale from the domain.

Practice

1. What is the main purpose of domain routing for locales in Next.js?

easy

A. To enable client-side routing only

B. To improve server performance by caching

C. To create multiple apps in one project

D. To serve different languages on different domains

Solution

1. Step 1: Understand domain routing concept

   Domain routing allows serving different languages or locales on separate domains or subdomains.

2. Step 2: Identify the main use case in Next.js

   Next.js uses domain routing to link domains to specific locales for internationalization.

3. Final Answer:

   To serve different languages on different domains -> Option D

4. Quick Check:

   Domain routing = serve languages on domains [OK]

Hint: Domain routing connects domains to languages [OK]

Common Mistakes:

• Confusing domain routing with caching
• Thinking it only affects client-side routing
• Assuming it creates multiple apps

2. Which Next.js config property is used to define domain routing for locales?

easy

A. routing.locales

B. i18n.domains

C. locales.domains

D. next.config.domains

Solution

1. Step 1: Recall Next.js i18n config structure

   The internationalization config uses the i18n key in next.config.js.

2. Step 2: Identify the property for domain routing

   The correct property to define domain-locale mapping is i18n.domains.

3. Final Answer:

   i18n.domains -> Option B

4. Quick Check:

   Domain routing config = i18n.domains [OK]

Hint: Look inside i18n config for domains key [OK]

Common Mistakes:

• Using next.config.domains instead of i18n.domains
• Confusing with routing.locales
• Trying to set domains outside i18n

3. Given this Next.js i18n config snippet, what locale will be served for requests to https://example.fr?

i18n: {
  locales: ['en', 'fr'],
  defaultLocale: 'en',
  domains: [
    { domain: 'example.com', defaultLocale: 'en' },
    { domain: 'example.fr', defaultLocale: 'fr' }
  ]
}

medium

A. fr

B. en

C. defaultLocale from browser

D. No locale, error occurs

Solution

1. Step 1: Check domain-locale mapping in config

   The domain example.fr is mapped to fr locale explicitly.

2. Step 2: Determine locale served for example.fr

   Requests to example.fr will serve the French locale fr.

3. Final Answer:

   fr -> Option A

4. Quick Check:

   example.fr domain = fr locale [OK]

Hint: Match domain to locale in i18n.domains array [OK]

Common Mistakes:

• Assuming defaultLocale 'en' applies to all domains
• Thinking browser locale overrides domain
• Believing error occurs without explicit locale

4. You wrote this middleware to detect locale by domain but it always serves the default locale. What is the likely mistake?

export function middleware(request) {
  const hostname = request.headers.get('host')
  if (hostname === 'example.fr') {
    return NextResponse.rewrite(new URL('/fr', request.url))
  }
  return NextResponse.next()
}

medium

A. Rewriting to '/fr' instead of setting locale cookie

B. Not returning a response for all domains

C. Using 'host' header instead of 'x-forwarded-host'

D. Middleware missing 'export default'

Solution

1. Step 1: Understand middleware role in locale detection

   Middleware should set locale or rewrite URL to include locale prefix properly.

2. Step 2: Identify issue with rewriting only

   Rewriting to '/fr' alone may not set locale context; locale cookie or header is needed for Next.js to recognize locale.

3. Final Answer:

   Rewriting to '/fr' instead of setting locale cookie -> Option A

4. Quick Check:

   Middleware must set locale, not just rewrite URL [OK]

Hint: Middleware must set locale, not just rewrite URL [OK]

Common Mistakes:

• Assuming host header is wrong
• Forgetting to handle all domains
• Missing export default in middleware

5. How would you configure Next.js to serve English on 'example.com' and French on 'example.fr' using domain routing, ensuring the default locale is English and URLs do not show locale prefixes?

hard

A. Set i18n.locales to ['en', 'fr'], defaultLocale to 'en', and i18n.domains with domains for example.com (fr) and example.fr (en), and use localeDetection: true

B. Set i18n.locales to ['en', 'fr'], defaultLocale to 'fr', and i18n.domains with domains for example.com (fr) and example.fr (en), and use localeDetection: true

C. Set i18n.locales to ['en', 'fr'], defaultLocale to 'en', and i18n.domains with domains for example.com (en) and example.fr (fr), and use localeDetection: false

D. Set i18n.locales to ['en', 'fr'], defaultLocale to 'en', and no domains, rely on middleware only

Solution

1. Step 1: Define locales and defaultLocale correctly

   Locales should be ['en', 'fr'] with defaultLocale 'en' to serve English by default.

2. Step 2: Configure i18n.domains for domain-locale mapping

   Map 'example.com' to 'en' and 'example.fr' to 'fr' in i18n.domains array.

3. Step 3: Disable localeDetection to avoid prefix in URLs

   Setting localeDetection: false prevents Next.js from adding locale prefixes in URLs, serving clean domain-based locales.

4. Final Answer:

   Set i18n.locales to ['en', 'fr'], defaultLocale to 'en', and i18n.domains with domains for example.com (en) and example.fr (fr), and use localeDetection: false -> Option C

5. Quick Check:

   Domain routing + defaultLocale + no prefix = Set i18n.locales to ['en', 'fr'], defaultLocale to 'en', and i18n.domains with domains for example.com (en) and example.fr (fr), and use localeDetection: false [OK]

Hint: Use i18n.domains and disable localeDetection for clean URLs [OK]

Common Mistakes:

• Swapping locales for domains
• Forgetting to disable localeDetection
• Relying only on middleware without domains