Sub-path routing for locales in NextJS

Introduction

Sub-path routing for locales helps show your website in different languages by using parts of the URL. It makes it easy for visitors to see content in their language.

You want to support multiple languages on your website.

You want URLs like /en/about or /fr/about to show content in English or French.

You want search engines to understand your site has different language versions.

You want to keep your site organized by language using URL paths.

You want users to switch languages by changing the URL path.

Syntax

NextJS

export const nextConfig = {
  i18n: {
    locales: ['en', 'fr', 'es'],
    defaultLocale: 'en',
    localeDetection: true
  }
};

The locales array lists all supported languages.

The defaultLocale is the language shown when no locale is specified.

Examples

This config supports English and French. English is the default language.

NextJS

i18n: {
  locales: ['en', 'fr'],
  defaultLocale: 'en'
}

This config supports English, French, and German. French is the default language.

NextJS

i18n: {
  locales: ['en', 'fr', 'de'],
  defaultLocale: 'fr'
}

Sample Program

This Next.js component shows the current language and available languages using sub-path routing. The config sets English, French, and Spanish as supported languages with English as default.

NextJS

import { useRouter } from 'next/router';

export default function Home() {
  const { locale, locales, defaultLocale, asPath } = useRouter();

  return (
    <main>
      <h1>Welcome!</h1>
      <p>Current language: {locale}</p>
      <p>Default language: {defaultLocale}</p>
      <p>Available languages: {locales.join(', ')}</p>
      <p>Current path: {asPath}</p>
    </main>
  );
}

// next.config.js
const nextConfig = {
  i18n: {
    locales: ['en', 'fr', 'es'],
    defaultLocale: 'en'
  }
};

export default nextConfig;

Important Notes

When you visit /fr, the page shows French content automatically.

Make sure to add translations for each locale in your app.

Locale detection can be turned on or off to control automatic language selection.

Summary

Sub-path routing uses URL parts like /en or /fr to show different languages.

Configure supported languages in next.config.js under i18n.

Use Next.js router to get current locale and show language-specific content.

Practice

1. What is the main purpose of sub-path routing for locales in Next.js?

easy

A. To create separate apps for each language without sharing code.

B. To serve different language versions of the site using URL prefixes like /en or /fr.

C. To load all languages at once on the homepage.

D. To disable internationalization features in Next.js.

Solution

1. Step 1: Understand sub-path routing concept

   Sub-path routing uses URL parts like /en or /fr to show different language versions of the same site.

2. Step 2: Compare options

   Only To serve different language versions of the site using URL prefixes like /en or /fr. correctly describes this purpose. Other options describe unrelated or incorrect behaviors.

3. Final Answer:

   To serve different language versions of the site using URL prefixes like /en or /fr. -> Option B

4. Quick Check:

   Sub-path routing = URL prefixes for languages [OK]

Hint: Remember: sub-path routing adds language code in URL path [OK]

Common Mistakes:

• Thinking sub-path routing loads all languages at once
• Confusing sub-path routing with separate apps per language
• Believing it disables i18n features

2. Which is the correct way to configure supported locales in next.config.js for sub-path routing?

easy

A. "i18n: ['en', 'fr'], defaultLocale: 'en'"

B. "locales: ['en', 'fr'], default: 'en'"

C. "i18n: { languages: ['en', 'fr'], defaultLang: 'en' }"

D. "i18n: { locales: ['en', 'fr'], defaultLocale: 'en' }"

Solution

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

   The correct config uses the i18n object with locales array and defaultLocale string.

2. Step 2: Match options to correct syntax

   "i18n: { locales: ['en', 'fr'], defaultLocale: 'en' }" matches the exact syntax. Others use wrong keys or structure.

3. Final Answer:

   "i18n: { locales: ['en', 'fr'], defaultLocale: 'en' }" -> Option D

4. Quick Check:

   i18n config = locales + defaultLocale [OK]

Hint: Look for 'i18n' key with 'locales' and 'defaultLocale' [OK]

Common Mistakes:

• Using wrong keys like 'languages' or 'defaultLang'
• Not wrapping locales inside 'i18n' object
• Using arrays without keys

3. Given this Next.js page code snippet, what will be rendered if the URL is /fr?

import { useRouter } from 'next/router';
export default function Home() {
  const { locale } = useRouter();
  return <div>Current language: {locale}</div>;
}

medium

A. Current language: undefined

B. Current language: en

C. Current language: fr

D. Error: useRouter() not found

Solution

1. Step 1: Understand useRouter locale property

   The useRouter hook provides the current locale from the URL sub-path like /fr.

2. Step 2: Match URL to locale value

   Since URL is /fr, locale will be 'fr', so the rendered text is "Current language: fr".

3. Final Answer:

   Current language: fr -> Option C

4. Quick Check:

   URL /fr sets locale = 'fr' [OK]

Hint: Locale matches URL sub-path prefix [OK]

Common Mistakes:

• Assuming default locale always shows
• Thinking locale is undefined without explicit code
• Confusing useRouter hook usage

4. Identify the error in this Next.js next.config.js snippet for locale sub-path routing:

module.exports = {
  i18n: {
    locales: ['en', 'fr'],
    defaultLocale: 'en',
    localeDetection: true,
  },
};

medium

A. The config is correct and will enable sub-path routing with locale detection.

B. localeDetection is not a valid option inside i18n.

C. locales must include the default locale twice.

D. localeDetection should be localeDetection: false to enable sub-path routing.

Solution

1. Step 1: Check valid i18n config options

   Next.js supports localeDetection inside i18n to enable or disable automatic locale detection.

2. Step 2: Verify given config

   The config has valid keys and values. Setting localeDetection: true enables automatic detection, which is allowed.

3. Final Answer:

   The config is correct and will enable sub-path routing with locale detection. -> Option A

4. Quick Check:

   localeDetection is valid and true means enabled [OK]

Hint: Check Next.js docs for valid i18n keys [OK]

Common Mistakes:

• Thinking localeDetection is invalid
• Believing localeDetection must be false for sub-path routing
• Duplicating default locale in locales array

5. You want to create a Next.js app supporting English and French with sub-path routing. You want the default locale to be English and URLs like /fr/about to show French content. Which steps are needed to correctly configure this? A) Set i18n.locales to ['en', 'fr'] and defaultLocale to 'en' in next.config.js. B) Use useRouter() in pages to get locale and show language-specific content. C) Create folders or files under app or pages to handle routes for each locale. D) Disable locale detection to force manual locale switching.

hard

A. Only A, B, and C are needed.

B. All A, B, C, and D are needed.

C. Only A and B are needed.

D. Only B and D are needed.

Solution

1. Step 1: Configure locales and defaultLocale

   Setting i18n.locales and defaultLocale in next.config.js enables sub-path routing for English and French.

2. Step 2: Use useRouter to get locale and show content

   Using useRouter() to get locale helps render language-specific content dynamically.

3. Step 3: Organize routes for each locale

   Creating folders or files under app or pages supports localized routes like /fr/about.

4. Step 4: Evaluate locale detection setting

   Disabling locale detection is optional and not required to support sub-path routing correctly.

5. Final Answer:

   Only A, B, and C are needed. -> Option A

6. Quick Check:

   Locales config + useRouter + route files = correct setup [OK]

Hint: Remember: locale config + router + route files are key [OK]

Common Mistakes:

• Thinking disabling locale detection is mandatory
• Not creating route files for localized paths
• Ignoring useRouter for locale detection