Domain routing for locales in NextJS - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is domain routing for locales in Next.js?

Domain routing for locales lets you serve different languages or regions from different domains or subdomains automatically based on the user's locale.

beginner

How do you configure domain routing for locales in Next.js?

You add a 'domains' array inside the 'i18n' config in next.config.js. Each domain object specifies the domain name and the defaultLocale it serves.

intermediate

Example of a domain configuration for French locale on 'example.fr'?

In next.config.js: { domains: [{ domain: 'example.fr', defaultLocale: 'fr' }] } inside the i18n config.

intermediate

What happens if a user visits a domain not listed in the domain routing config?

Next.js falls back to the default locale and domain specified in the i18n config or redirects based on your setup.

intermediate

Why use domain routing for locales instead of path-based locale routing?

Domain routing provides a cleaner URL without locale prefixes and can improve SEO by targeting specific country domains.

Where do you configure domain routing for locales in Next.js?

A public folder

B pages/_app.js

C next-env.d.ts

D next.config.js inside the i18n object

Domain routing for locales is set inside the i18n configuration in next.config.js.

What key do you use to specify the domain for a locale in Next.js config?

A localeDomain

B domain

C host

D site

The key 'domain' specifies the domain name for a locale in the domains array.

If you want 'example.de' to serve German content, how do you specify it?

A { domain: 'example.de', defaultLocale: 'de' }

B { domain: 'de.example.com', locale: 'de' }

C { host: 'example.de', locale: 'de' }

D { domain: 'example.de', locale: 'en' }

You specify the domain and defaultLocale like { domain: 'example.de', defaultLocale: 'de' }.

What benefit does domain routing provide over path-based locale routing?

A Shorter URLs without locale prefixes

B Slower page loads

C Requires no configuration

D Works only on localhost

Domain routing gives cleaner URLs without locale prefixes like /en or /fr.

What happens if a user visits a domain not configured for any locale?

A The site crashes

B User is redirected to Google

C Next.js uses the default locale

D The page shows a 404 error

Next.js falls back to the default locale if the domain is not configured.

Explain how to set up domain routing for locales in a Next.js project.

Think about where Next.js config lives and how locales are defined.

Describe the advantages of using domain routing for locales compared to path-based locale routing.

Consider URL appearance and search engine benefits.

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