Next.js internationalization (i18n) tutorial

All code samples used in this section are available on the GitHub repo.

Create a new Next.js project

First, let's create a new Next.js project with the create-next-app CLI tool. This tool is maintained by the creators of Next.js and will make the creation process easier for us. By running the command below, we will create a new Next.js project called nextjs-app-router-i18n-example in a directory with the same name.

npx create-next-app@latest nextjs-app-router-i18n-example

Since this command operates in interactive mode, we will go with the default settings for the sake of this tutorial.

Would you like to use TypeScript? [Yes]
Would you like to use ESLint? [Yes]
Would you like to use Tailwind CSS? [No]
Would you like to use `src/` directory? [Yes]
Would you like to use App Router? (recommended) [Yes]
Would you like to customize the default import alias (@/*)? [No]

Add React Intl dependency

Next.js works well with most i18n libraries (react-intl, lingui, next-intl, and similar). For this guide, React Intl is our choice due to its wide use and advanced features such as ICU syntax. To add it, enter the nextjs-app-router-i18n-example directory and install the react-intl.

cd nextjs-app-router-i18n-example
npm i react-intl

Add config for internationalized routing

Configuring internationalized routing in apps based on App Router is not completely automated and requires a bit of manual work. To start, let's first create an i18n-config.ts file in the root of the project and fill it with our i18n configuration. The locales represent the list of locales we would like to support in our app, and the defaultLocale represents the default locale of the app, and the one that will be used when visiting non-locale-prefixed paths.

The i18n-config.ts file:

export const i18n = {
  locales: ["en", "ar", "fr", "nl-NL"],
  defaultLocale: "en",
};

export type I18nConfig = typeof i18n;
export type Locale = I18nConfig["locales"][number];

After creating the configuration file, the next step involves updating the app directory to support internationalized routing. To accomplish this, we need to put all page files within the [locale] directory. That way, app pages will have access to the currently used locale and be able to display appropriate localization messages.

nextjs-app-router-i18n-example
|-- public
|-- src
|   |-- app
|   |   |-- [locale]
|   |   |   |-- globals.css
|   |   |   |-- layout.tsx
|   |   |   |-- page.module.css
|   |   |   |-- page.tsx
|   |   |-- favicon.ico
|-- ...
|-- i18n-config.ts
|-- next.config.js
|-- package.json
|-- package-lock.json

Create localization files

The next step is to add localization files. For that purpose, let's create a lang directory within the src directory. Inside it, add four JSON files named ar.json, en.json, fr.json, and nl-NL.json. These files will contain the translations for Arabic, English, French, and Dutch (Netherlands), respectively.

Afterward, fill in localization files with messages that we will use later.

The ar.json file:

{
  "common.footer": "دروس التدويل",
  "page.home.head.title": "مثال على Next.js i18n",
  "page.home.head.meta.description": "مثال Next.js i18n - عربي",
  "page.home.title": "مرحبًا بك في <b> البرنامج التعليمي Next.js i18n </b>",
  "page.home.description": "أنت الآن تستعرض الصفحة الرئيسية بالعربية 🚀"
}

The en.json file:

{
  "common.footer": "internationalization tutorial",
  "page.home.head.title": "Next.js i18n example",
  "page.home.head.meta.description": "Next.js i18n example - English",
  "page.home.title": "Welcome to <b>Next.js i18n tutorial</b>",
  "page.home.description": "You are currently viewing the homepage in English 🚀"
}

The fr.json file:

{
  "common.footer": "tutoriel d'internationalisation",
  "page.home.head.title": "Next.js i18n exemple",
  "page.home.head.meta.description": "Next.js i18n exemple - Français",
  "page.home.title": "Bienvenue à <b>Next.js i18n didacticiel</b>",
  "page.home.description": "Vous consultez actuellement la page d'accueil en Français 🚀"
}

The nl-NL.json file:

{
  "common.footer": "handleiding internationalisering",
  "page.home.head.title": "Next.js i18n voorbeeld",
  "page.home.head.meta.description": "Next.js i18n voorbeeld - Nederlands (Nederland)",
  "page.home.title": "Welkom bij <b>Next.js i18n zelfstudie</b>",
  "page.home.description": "U bekijkt momenteel de homepage in het Nederlands (Nederland) 🚀"
}

Configure react-intl in Next.js project

Configuring React Intl with Next.js largely depends on how localization messages are used and whether they need to be accessed on the server side or the client side. Knowing that Next.js is a highly flexible framework, and that typical usage mostly combines both server-side and client-side approaches, in the following sections we will cover both approaches in more detail.

Server components

The use of server components in Next.js offers several advantages, such as the ability to render UI components on the server, reduce the time needed to fetch data for rendering, caching, and similar tasks. However, these components are distinct from traditional client-side components as they lack access to certain React features like context providers and side effects.

When it comes to the React Intl library and its usage for server-side rendering, an alternative method must be used to access localization messages since this library relies on the provider pattern. To overcome this limitation, we will create a lib directory in our project's src directory. Within this lib directory, we will create a file named intl.ts. In this file, we will define a function called getIntl that will use the core functionality of the React Intl library to access localization messages, allowing us to circumvent these limitations.

The intl.ts file:

import "server-only";

import { createIntl } from "@formatjs/intl";
import type { Locale } from "../../i18n-config";

export async function getIntl(locale: Locale) {
  return createIntl({
    locale: locale,
    messages: (await import(`../lang/${locale}.json`)).default,
  });
}

Client components

Just as server components have their benefits, client components do too. They facilitate the development of interactive elements utilizing event handlers, states, effects, and similar functions, as well as the browser API.

In order to use the React Intl library in client components, we first need to set up the IntlProvider. For that purpose, we will add a components directory within the src directory. Inside the components directory, let's create a Footer directory, and add two files within it, namely FooterContainer.tsx and Footer.tsx.

Below, you will find a FooterContainer component that loads localization messages and configures the IntlProvider, enabling child components to easily access the appropriate localization messages.

The FooterContainer.tsx file:

import React from "react";
import { IntlProvider } from "react-intl";

async function getMessages(locale: string) {
  return await import(`../../lang/${locale}.json`);
}

type FooterContainerProps = {
  locale: string;
  children: React.ReactNode;
};

async function FooterContainer({ locale, children }: FooterContainerProps) {
  const messages = await getMessages(locale);

  return (
    <IntlProvider locale={locale} messages={messages}>
      <div className="footer">{children}</div>
    </IntlProvider>
  );
}

export default FooterContainer;

The Footer component displayed below is a client component that accesses localization messages declaratively using the FormattedMessage component.

The Footer.tsx file:

"use client";

import { FormattedMessage } from "react-intl";

import FooterContainer from "./FooterContainer";

function Footer({ locale }: { locale: string }) {
  return (
    <FooterContainer locale={locale}>
      <div>
        <FormattedMessage tagName="p" id="common.footer" />
      </div>
    </FooterContainer>
  );
}

export default Footer;

Adapt pages for i18n

Now when we have created a way to access localization messages on the server side and on the client side, let's merge these pieces together in our Home page.

First, let's update the RootLayout component to properly set the lang attribute on the html element and to include the Footer component below the content of the Home page.

The layout.tsx file:

import Footer from "../../components/Footer/Footer";
import "./globals.css";

type LayoutProps = {
  params: { locale: string };
  children: React.ReactNode;
};

export default function RootLayout({ params, children }: LayoutProps) {
  const { locale } = params;

  return (
    <html lang={locale}>
      <body>
        {children}
        <Footer locale={locale} />
      </body>
    </html>
  );
}

Next, let's update Home page content so it also shows two localization messages.

The page.tsx file:

import { getIntl } from "../../lib/intl";
import styles from "./page.module.css";

type HomeProps = {
  params: { locale: string };
};

export default async function Home({ params: { locale } }: HomeProps) {
  const intl = await getIntl(locale);

  return (
    <div className={styles.container}>
      <main className={styles.main}>
        <h1 className={styles.title}>
          {intl.formatMessage(
            { id: "page.home.title" },
            { b: (chunks) => <b key="bold">{chunks}</b> }
          )}
        </h1>

        <p className={styles.description}>
          {intl.formatMessage({ id: "page.home.description" })}
        </p>
      </main>
    </div>
  );
}

Determine text direction

When it comes to text direction, languages can be ltr (Left-to-Right) or rtl (Right-to-Left). The default text direction in HTML is ltr. In most cases, you don't need to configure anything. However, when one of the languages is rtl, you need to set the proper text direction for your pages. In our case, Arabic is an rtl language, so we need to handle that. For that purpose, we extended the intl.ts file with the getDirection function. This function returns the text direction for the passed locale. Later in the code, we will use that function and apply its response to set the appropriate dir attribute for the html element.

The intl.ts file:

import "server-only";

import { createIntl } from "@formatjs/intl";
import type { Locale } from "../../i18n-config";

export async function getIntl(locale: Locale) { ... }

export function getDirection(locale: Locale) {
  switch (locale) {
    case "ar":
      return "rtl";
    case "en":
    case "fr":
    case "nl-NL":
      return "ltr";
  }
}

Now that we've added a function that returns the appropriate text direction for a locale, let's use it in our app. The easiest way to set the text direction is to set it on the html element, as the directionality set here will propagate to all child elements in the HTML tree that do not have an explicitly set text directionality. For that purpose, let's update our RootLayout component with text directionality.

The layout.tsx file:

import Footer from "../../components/Footer/Footer";
import { getDirection } from "../../lib/intl";
import "./globals.css";

type LayoutProps = {
  params: { locale: string };
  children: React.ReactNode;
};

export default function RootLayout({ params, children }: LayoutProps) {
  const { locale } = params;

  const dir = getDirection(locale);

  return (
    <html lang={locale} dir={dir}>
      <body>
        {children}
        <Footer locale={locale} />
      </body>
    </html>
  );
}

Add hreflang tags

The hreflang tag is a way to tell search engines which language you are using on a specific page, as well as the other language variants of that page. Doing so will help them present users with the most appropriate version of your page. In this post, we will not delve into the details of hreflang tags, but it should be noted that including them is a good practice for improved SEO. Also, ensure that href attribute values are updated to correspond with your domain. Additionally, for enhanced SEO and better keyword targeting, consider localizing the title and meta description of your page, as illustrated in the example below.

import { Metadata, ResolvingMetadata } from "next";

import { getIntl } from "../../lib/intl";
import styles from "./page.module.css";

type RouteProps = {
  params: { locale: string };
  searchParams: { [key: string]: string | string[] | undefined };
};

export async function generateMetadata(
  props: RouteProps,
  parent: ResolvingMetadata
): Promise<Metadata> {
  const intl = await getIntl(props.params.locale);

  return {
    title: intl.formatMessage({ id: "page.home.head.title" }),
    description: intl.formatMessage({
      id: "page.home.head.meta.description",
    }),
    alternates: {
      canonical: "https://example.com",
      languages: {
        ar: "http://example.com/ar",
        en: "http://example.com",
        fr: "http://example.com/fr",
        "nl-NL": "http://example.com/nl-NL",
        "x-default": "http://example.com",
      },
    },
  };
}

type HomeProps = { ... };

export default async function Home({ params: { locale } }: HomeProps) { ... }

Add language switcher

Incorporating a feature that allows users to change the language on the app is essential if we offer multilingual support. The ability to switch languages enhances the user's experience and satisfaction.

In this blog post, we're going to implement a basic language switcher. To do this, we will create a new Header directory alongside the existing Footer directory within the components directory. Within the Header directory, we will add a Header.tsx file, which will include the code for our basic language switching functionality.

The Header.tsx file:

import Link from "next/link";
import { i18n } from "../../../i18n-config";

function Header() {
  const { locales, defaultLocale } = i18n;

  return (
    <header>
      <div dir="ltr" className="languages">
        {[...locales].sort().map((locale) => (
          <Link
            key={locale}
            href={locale === defaultLocale ? "/" : `/${locale}`}
          >
            {locale}
          </Link>
        ))}
      </div>
    </header>
  );
}

export default Header;

Having created the language switcher, it's time to embed it into our application by updating the RootLayout to encompass the Header component that features the language switcher.

The layout.tsx file:

import Header from "../../components/Header/Header";
import Footer from "../../components/Footer/Footer";
import { getDirection } from "../../lib/intl";
import "./globals.css";

type LayoutProps = { ... };

export default function RootLayout({ params, children }: LayoutProps) {
  const { locale } = params;

  const dir = getDirection(locale);

  return (
    <html lang={locale} dir={dir}>
      <body>
        <Header />
        {children}
        <Footer locale={locale} />
      </body>
    </html>
  );
}

Now, when we've configured most of the things, we could run our Next.js app. Running the following command will allow us to see how our app looks on the localhost.

npm run dev

http://localhost:3000/ ➝ Not found (fixed in upcoming chapter)

http://localhost:3000/ar ➝ Arabic

http://localhost:3000/fr ➝ French

http://localhost:3000/nl-NL ➝ Dutch (Netherlands)

Automatic locale detection

The automatic locale detection is a handy feature. It enables us to easily identify the user's preferred language from the Accept-Language header. This kind of functionality is not only related to web apps but is also used in other areas like mobile app development where the app preselects the language that best aligns with the user's phone settings.

To easily extract the user's preferred languages from the Accept-Language header, we will use the Negotiator library.

npm i negotiator
npm i @types/negotiator --save-dev

Now that we've added the required dependencies, let's create a middleware.ts file within the src directory. This file will contain middleware that will detect the language from the Accept-Language header and route to the appropriate page variant. Additionally, we will enhance this middleware to identify the default locale, and in the case of a request for the default locale, instruct the middleware to redirect to a path without a locale prefix.

The middleware.ts file:

import { NextResponse } from "next/server";
import type { NextRequest } from "next/server";

import { match } from "@formatjs/intl-localematcher";
import Negotiator from "negotiator";

import { i18n } from "../i18n-config";
import type { I18nConfig } from "../i18n-config";

function getLocale(request: NextRequest, i18nConfig: I18nConfig): string {
  const { locales, defaultLocale } = i18nConfig;

  const negotiatorHeaders: Record<string, string> = {};
  request.headers.forEach((value, key) => (negotiatorHeaders[key] = value));

  const languages = new Negotiator({ headers: negotiatorHeaders }).languages(
    locales
  );

  return match(languages, locales, defaultLocale);
}

export function middleware(request: NextRequest) {
  let response;
  let nextLocale;

  const { locales, defaultLocale } = i18n;

  const pathname = request.nextUrl.pathname;

  const pathLocale = locales.find(
    (locale) => pathname.startsWith(`/${locale}/`) || pathname === `/${locale}`
  );

  if (pathLocale) {
    const isDefaultLocale = pathLocale === defaultLocale;
    if (isDefaultLocale) {
      let pathWithoutLocale = pathname.slice(`/${pathLocale}`.length) || "/";
      if (request.nextUrl.search) pathWithoutLocale += request.nextUrl.search;

      response = NextResponse.redirect(new URL(pathWithoutLocale, request.url));
    }

    nextLocale = pathLocale;
  } else {
    const isFirstVisit = !request.cookies.has("NEXT_LOCALE");

    const locale = isFirstVisit ? getLocale(request, i18n) : defaultLocale;

    let newPath = `${locale}${pathname}`;
    if (request.nextUrl.search) newPath += request.nextUrl.search;

    response =
      locale === defaultLocale
        ? NextResponse.rewrite(new URL(newPath, request.url))
        : NextResponse.redirect(new URL(newPath, request.url));
    nextLocale = locale;
  }

  if (!response) response = NextResponse.next();

  if (nextLocale) response.cookies.set("NEXT_LOCALE", nextLocale);

  return response;
}

export const config = {
  matcher: "/((?!api|_next/static|_next/image|img/|favicon.ico).*)",
};

To check how this works, let's run the Next.js app on the localhost and try to open it with different browser settings.

1. Run the app on the localhost

npm run dev

2. Update browser language to Arabic, English, French, or Dutch (Netherlands)

3. Open the app in browser

Whenever we change the browser language and open http://localhost:3000, we will be redirected to the appropriate page.

Arabic ➝ http://localhost:3000/ar

French ➝ http://localhost:3000/fr

Dutch (Netherlands) ➝ http://localhost:3000/nl-NL

Other langauges ➝ http://localhost:3000

Keep selected language in cookie for future visits

It's important to acknowledge that Next.js simplifies the process of handling cookies within its middleware, providing a straightforward way to save the user's preferred language setting. This ensures that every subsequent request is informed of the user's language preference. While this tutorial has demonstrated how to save the preferred locale via cookies, we haven't explained how to redirect users to their preferred language pages based on cookie values. We'll bypass this aspect for now to maintain a simple tutorial structure.

Nevertheless, when deciding to leverage cookies for managing language settings, consider the following:

• Determine the optimal cookie duration for your scenario, whether it be for a session or a specified period such as a day or a month.
• Assess any complications that may arise with Next.js's caching mechanisms.
• Ensure your application can effectively determine the user's preferred language, particularly when there's a discrepancy between the locale indicated by the cookie and the one suggested by the Accept-Language header.

Static HTML export

Web apps don't always require databases or servers; many websites function optimally with only static files, which are simple to host and often cost little to nothing. In the end, it all depends on the purpose for which the website is used. The Next.js framework supports static exports. Below are two code snippets that would allow us to generate static HTML files in our Next.js project. It's important to recognize, though, that with these snippets, static HTML files are the only result; dynamic features like user redirection or detection of Accept-Language header aren't possible. While there are some solutions and workarounds to these limitations, this guide will not explore them in order to keep things simple and straightforward.

The next.conig.js file:

/** @type {import('next').NextConfig} */
const nextConfig = {
  output: "export",
};

module.exports = nextConfig;

The page.tsx file:

import { Metadata, ResolvingMetadata } from "next";

import { getIntl } from "../../lib/intl";
import { i18n } from "../../../i18n-config";
import styles from "./page.module.css";

type RouteProps = { ... };

export async function generateMetadata( ... ): Promise<Metadata> { ... }

type HomeProps = { ... };

export default async function Home({ params: { locale } }: HomeProps) { ... }

export async function generateStaticParams() {
  const { locales } = i18n;

  return locales.map((locale) => ({
    locale: locale,
  }));
}

All code samples used in this section are available on the GitHub repo.

Create a new Next.js project

First, let's create a new Next.js project with the create-next-app CLI tool. This tool is maintained by the creators of Next.js and will make the creation process easier for us. By running the command below, we will create a new Next.js project called nextjs-i18n-example in a directory with the same name.

npx create-next-app@latest nextjs-i18n-example

Since this command operates in interactive mode, we will go with the following settings for the sake of this tutorial.

Would you like to use TypeScript? [No]
Would you like to use ESLint? [Yes]
Would you like to use Tailwind CSS? [No]
Would you like to use `src/` directory? [No]
Would you like to use App Router? (recommended) [No]
Would you like to customize the default import alias (@/*)? [No]

Add React Intl dependency

As we mentioned earlier, the Next.js works well with existing i18n libraries (react-intl, lingui, next-intl, and similar). In this tutorial, we will use the react-intl. This library is one of the most popular in the context of internationalization. It supports ICU syntax and various formatting options. By running the commands below, we will change the current working directory to the nextjs-i18n-example and install the react-intl dependency.

cd nextjs-i18n-example
npm i react-intl

Add config for internationalized routing

Translations and routing are two main pillars of internationalization. The previously added react-intl library is going to handle translations and formatting. When it comes to routing, Next.js has built-in support for that. This built-in support offers two options, sub-path routing, and domain routing. As the names imply, sub-path routing uses the locale in the url path, whereas domain routing uses different domains for serving content for different locales. In our case, we will use sub-path routing as it is less complex and more common for average websites.

Sub-path routing examples

• /blog
• /fr/blog
• /nl-NL/blog

Domain routing examples

• example.com/blog
• example.fr/blog
• example.nl/blog

To use the built-in support for internationalized routing, we need to update the next.config.js file with the i18n config. The locales represents the list of locales we are going to support in our app. The defaultLocale represents the default locale of the app. That means that all pages for Arabic, French, and Dutch (Netherlands) will be prefixed with the ar, fr, and nl-NL in url path.

The next.config.js file:

/** @type {import('next').NextConfig} */
const nextConfig = {
  reactStrictMode: true,
  i18n: {
    // The locales you want to support in your app
    locales: ["ar", "en", "fr", "nl-NL"],
    // The default locale you want to be used when visiting a non-locale prefixed path e.g. `/hello`
    defaultLocale: "en",
  },
};

module.exports = nextConfig;

Automatic Locale Detection

The above-added config for the internationalized routing by default includes automatic locale detection. That means that Next.js will try to automatically detect which locale the user prefers based on the Accept-Language header. To check how this works, let's run the Next.js app on the localhost and try to open it with different browser settings.

1. Run the app on the localhost

npm run dev

2. Update browser language to Arabic, English, French, or Dutch (Netherlands)

3. Open the app in browser

Whenever we change the browser language and open http://localhost:3000, we will be redirected to the appropriate page.

Arabic ➝ http://localhost:3000/ar

French ➝ http://localhost:3000/fr

Dutch (Netherlands) ➝ http://localhost:3000/nl-NL

Other langauges ➝ http://localhost:3000

In some rare cases, you might want to disable automatic locale detection. To achieve that, you should set the localeDetection to false in the next.config.js file. After that, Next.js will no longer automatically redirect based on the user's preferred locale.

The next.config.js file:

...
const nextConfig = {
  ...
  i18n: {
    ...
    localeDetection: false
  },
};
...

Create localization files

The next important thing is to add localization files. For that purpose, let's create a lang directory. Within it, add four JSON files: ar.json, en.json, fr.json, and nl-NL.json. These files are going to hold translations for Arabic, English, French, and Dutch (Netherlands), respectively. Below, you can see the project structure after adding the mentioned files.

nextjs-i18n-example
|-- lang
|   |-- ar.json
|   |-- en.json
|   |-- fr.json
|   |-- nl-NL.json
|-- pages
|   |-- api
|   |-- _app.js
|   |-- index.js
|   |-- ...
|-- public
|-- ...
|-- package.json
|-- package-lock.json

Afterward, fill in localization files with messages that we will use later.

The ar.json file:

{
  "page.home.head.title": "مثال على Next.js i18n",
  "page.home.head.meta.description": "مثال Next.js i18n - عربي",
  "page.home.title": "مرحبًا بك في <b> البرنامج التعليمي Next.js i18n </b>",
  "page.home.description": "أنت الآن تستعرض الصفحة الرئيسية بالعربية 🚀"
}

The en.json file:

{
  "page.home.head.title": "Next.js i18n example",
  "page.home.head.meta.description": "Next.js i18n example - English",
  "page.home.title": "Welcome to <b>Next.js i18n tutorial</b>",
  "page.home.description": "You are currently viewing the homepage in English 🚀"
}

The fr.json file:

{
  "page.home.head.title": "Next.js i18n exemple",
  "page.home.head.meta.description": "Next.js i18n exemple - Français",
  "page.home.title": "Bienvenue à <b>Next.js i18n didacticiel</b>",
  "page.home.description": "Vous consultez actuellement la page d'accueil en Français 🚀"
}

The nl-NL.json file:

{
  "page.home.head.title": "Next.js i18n voorbeeld",
  "page.home.head.meta.description": "Next.js i18n voorbeeld - Nederlands (Nederland)",
  "page.home.title": "Welkom bij <b>Next.js i18n zelfstudie</b>",
  "page.home.description": "U bekijkt momenteel de homepage in het Nederlands (Nederland) 🚀"
}

Configure react-intl in Next.js project

Internationalized routing and localization files are just the first part of the task. The second part is setting up the react-intl library. Below, you can see what changes have been made in the _app.js file.

Wrap the app with the IntlProvider

The react-intl uses the provider pattern for passing the i18n context to a tree of components. Therefore, we will need to wrap the app's root with the IntlProvider. Using the useRouter hook, we can access the locale information and pass appropriate localization messages to the IntlProvider.

Determine text direction

When it comes to the text direction, languages can be ltr (left-to-right) or rtl (right-to-left). The default text direction in HTML is ltr. In most cases, you don't need to configure anything. However, when one of the languages is rtl, you might need to handle text direction explicitly. In our case, Arabic is the rtl, so we need to handle that as well. For that purpose, we added the getDirection function. It returns the text direction for the passed locale. Later in the code, we will use that function and pass its response as dir prop to all pages in our app.

Note that this is not the only way for setting the text direction in Next.js apps. Alternatively, you could handle that in the _document.js file by updating the dir attribute of the html element or in your Layout component. For the sake of simplicity, we put that logic inside the _app.js file. However, you should use the approach that works best for you.

The _app.js file:

import { useRouter } from "next/router";
import { IntlProvider } from "react-intl";

import ar from "../lang/ar.json";
import en from "../lang/en.json";
import fr from "../lang/fr.json";
import nl_NL from "../lang/nl-NL.json";

import "../styles/globals.css";

const messages = {
  ar,
  en,
  fr,
  "nl-NL": nl_NL,
};

function getDirection(locale) {
  if (locale === "ar") {
    return "rtl";
  }

  return "ltr";
}

function MyApp({ Component, pageProps }) {
  const { locale } = useRouter();

  return (
    <IntlProvider locale={locale} messages={messages[locale]}>
      <Component {...pageProps} dir={getDirection(locale)} />
    </IntlProvider>
  );
}

export default MyApp;

Adapt pages for i18n

We did most of the work. The last step is to put all this together. Therefore, we are going to update the index.js file under the pages directory. Below, you can find two approaches for accessing the localization messages, imperative and declarative. We've already covered these two ways of usage, formatting options, and similar in another post. Therefore, we will not spend more words on that. Instead, we are going to focus on the hreflang tag, language switcher, and other important things.

Add hreflang tags

The hreflang tag is a way to tell search engines which language you are using on a specific page. Doing so will help them to show users the most appropriate version of your page. In this post, we will not go into depth regarding hreflang, but it should be noted that it is good practice to include them for better SEO. Also, keep in mind that href attribute values need to be updated to correspond to your domain.

Add language switcher

When it comes to the language switcher, we've used the useRouter hook to retrieve locales information. Later, we've mapped each locale to a Link component. The Link component accepts the optional locale prop for transitioning to a different locale from the currently active one. If not provided, the locale prop will use the currently active locale.

Keep selected language in cookie for future visits

It is worth noting that Next.js allows you also to store selected locale in the NEXT_LOCALE cookie. That cookie can be used later for overriding the Accept-Language header (Automatic Locale Detection) by redirecting the user to the correct location. That is, the user that prefers the locale en in the Accept-Language header, but has a NEXT_LOCALE=fr cookie, will be redirected to a page that corresponds to fr locale. In this tutorial, we did not use this cookie. However, its implementation is not complicated. Whenever the user changes the language, the mentioned cookie should be updated.

Set text direction

As for the text direction, we just need to set the dir prop of the Home component to the container of our content. As we stated earlier, this is just one way to solve it. Feel free to use the method that works best for you.

The index.js file:

import Head from "next/head";
import Link from "next/link";
import { useRouter } from "next/router";
import { FormattedMessage, useIntl } from "react-intl";

import styles from "../styles/Home.module.css";

export default function Home({ dir }) {
  const { locales } = useRouter();

  const intl = useIntl();

  const title = intl.formatMessage({ id: "page.home.head.title" });
  const description = intl.formatMessage({ id: "page.home.head.meta.description" });

  return (
    <div className={styles.container}>
      <Head>
        <title>{title}</title>
        <meta name="description" content={description} />
        <link rel="icon" href="/favicon.ico" />

        {/* Add hreflang links */}
        <link rel="alternate" href="http://example.com" hrefLang="x-default" />
        <link rel="alternate" href="http://example.com" hrefLang="en" />
        <link rel="alternate" href="http://example.com/ar" hrefLang="ar" />
        <link rel="alternate" href="http://example.com/fr" hrefLang="fr" />
        <link rel="alternate" href="http://example.com/nl-NL" hrefLang="nl-NL" />
      </Head>

      <header>
        <div className={styles.languages}>
          {[...locales].sort().map((locale) => (
            <Link key={locale} href="/" locale={locale}>
              {locale}
            </Link>
          ))}
        </div>
      </header>

      <main dir={dir} className={styles.main}>
        <h1 className={styles.title}>
          <FormattedMessage id="page.home.title" values={{ b: (chunks) => <b>{chunks}</b> }} />
        </h1>

        <p className={styles.description}>
          <FormattedMessage id="page.home.description" />
        </p>
      </main>
    </div>
  );
}

Congratulations! 🎉
You have successfully set up internationalization in your Next.js project.
If you have followed all the steps, your app should look like the one shown below.

What about static HTML export?

Currently, the biggest weakness of the internationalization of Next.js apps is the inability to export to static HTML. Running such command results in "Error: i18n support is not compatible with next export". This issue has already been reported and discussed. A potential workaround would be to use a regular Next.js deployment strategy or manual handling of i18n routing.