Nextjs i18n: A Comprehensive Guide

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Nextjs i18n is a game-changer for developers who want to create multilingual websites. With its built-in support for internationalization (i18n), you can easily translate your content and reach a wider audience.

Nextjs i18n allows you to separate your translation data from your application code. This makes it easier to manage and update translations without affecting the rest of your application.

By using Nextjs i18n, you can create a seamless user experience for visitors who speak different languages. Your website will automatically detect the user's language preference and display the corresponding content.

The i18n feature also enables you to handle complex translation scenarios, such as pluralization and date formatting.

Getting Started

To get started with Next.js i18n, you'll need to install the `i18next` library and the `react-i18next` adapter. This will allow you to manage translations for your application.

Next.js provides a built-in support for internationalization, but you'll need to configure it by creating a new file called `i18n.js` in the root of your project.

In this file, you'll need to specify the supported languages and the default language for your application. For example, you might add the following code: `export default { supportedLngs: ['en', 'fr'], defaultLng: 'en' }`.

This configuration will enable i18n support for your application, allowing users to switch between languages.

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Installation and Setup

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To set up next-intl, you'll need to install the NPM package from the command line. This involves running the command to install the package, which we've covered before.

Next, you'll need to create a few setup files to get next-intl working smoothly. This includes adding a plugin to your next.config.mjs file and creating a new file called i18n.config.ts at the root of your project to house your config.

The i18n.ts configuration file is also important, as it loads translations for next-intl. By default, this file must be in the project route and called i18n.ts, although this is configurable.

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Installing Next-Intl

Installing Next-Intl is a straightforward process that can be completed in a few simple steps. First, you'll need to install the next-intl NPM package from the command line, which we covered in our previous setup.

You can install next-intl by running a command in your terminal, which is a great way to get started with localization. This is a crucial step in the process, and it's essential to get it right.

To install next-intl, you'll need to use the npm package manager. This is a common tool used by developers to manage dependencies and packages in their projects. Our Header component needs its navigation links localized anyway, so this is a good opportunity to get started.

Config File Setup

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To set up your config files, start by creating a new file called i18n.config.ts at the root of your project to house your config. This file will contain your app's supported locales.

You'll also need to create a next.config.mjs file and add a plugin to it to get next-intl working smoothly. This includes adding a plugin to your next.config.mjs file to enable localized routing.

Don't forget to create a middleware.ts file at the root of your project and set it up with some starter config. This middleware will help next-intl provide the necessary functionality for your app.

Next, create a next-i18next.config.js file in the root of your project and fill it with your i18n configuration. This file tells next-i18next what your defaultLocale and other locales are, so that it can preload translations on the server.

In this file, you'll need to specify the locales property, which is an array of languages you want your app to support. You'll also need to specify the defaultLocale property, which is the language that visitors will fall back to if your app does not support their language.

Lastly, create an i18n-config.ts file in the root of your project and fill it with your i18n configuration. This file should include the locales and defaultLocale properties, which will be used to support internationalized routing in your app.

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Internationalization Basics

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A basic test is a great way to get started with next-intl, and it's surprisingly easy. You can add translations to your components using the useTranslations hook.

This hook allows you to pull translations for the active locale using its returned t() function. You can access all translations in a file by calling useTranslations() with no params.

To test next-intl, you'll want to swap your new Server Component into your home page to see the changes in action. Visiting /en-us should look exactly as it did before, while visiting /ar-eg should display your app title in Arabic.

The useTranslations hook is a powerful tool for localizing your app. You can use it to pull translations for the active locale and access all translations in a file.

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Configuring Next-Intl

To configure next-intl, you'll need to install the next-intl NPM package from the command line. First things first, let's install the next-intl NPM package from the command line: We covered this when we configured and set up next-intl.

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Next, create a few small setup files to get next-intl working smoothly. This includes adding a plugin to your next.config.mjs file and creating a new file called i18n.config.ts at the root of your project to house your config. next-intl uses a special i18n.ts configuration file to load translations—not to be confused with the previous i18n.config.ts.

By default, this file must be in the project route and called i18n.ts, although this is configurable. One last boilerplate is wiring up a Next.js middleware that next-intl provides. Let's create a middleware.ts file at the root of your project and set it up with some starter config.

Consider reading: Nextjs Middleware Matcher

Create a Config

To create a config for your Next-Intl project, start by defining the locales property in your config file. This is an array of languages you want your app to support.

The defaultLocale property is the language that visitors will fall back to if your app doesn't support their language.

You can add more advanced configuration options by passing them via next-i18next.config.js if needed.

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Configuring Locale Prefix

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The locale prefix is a crucial part of configuring next-intl. By default, it uses a forced locale prefix, meaning routes like /about automatically redirect to /en-us/about. This makes localized routing consistent, but we can adjust it.

We can change the setting to as-needed, which means the default locale won't have a prefix, but all others will. With this setting, visiting / or /week directly shows content in the default English locale without the /en-us prefix.

To access content in Arabic, such as the weekly weather, we must explicitly use the ar-eg prefix, for example, /ar-eg/week. For this tutorial, we'll revert the prefix setting to the forced "always" mode.

We can also set localePrefix: "never" which disables prefixes entirely. This option relies on a cookie for determining the locale.

Advanced Topics

In Next.js i18n, you can use the `useTranslation` hook to access the current locale and translation functions.

The `useTranslation` hook returns an object with two properties: `t` and `i18n`. The `t` function is used to translate strings, while the `i18n` object provides information about the current locale.

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You can use the `useTranslation` hook in any component that needs to access the current locale and translation functions.

The `i18n` object also provides a `language` property that returns the current language code.

Next.js i18n supports server-side rendering, which means you can render pages with different languages on the server.

Server-side rendering is enabled by default in Next.js, but you can disable it if you need to.

To disable server-side rendering, you need to set the `target` option in your `next.config.js` file to `'static'`.

By disabling server-side rendering, you can improve performance and reduce the load on your server.

However, disabling server-side rendering may also affect SEO and user experience.

To improve performance, you can use code splitting to load only the necessary modules for each language.

Code splitting is a technique that allows you to split your code into smaller chunks and load them only when needed.

Next.js provides a built-in function called `getStaticPaths` that allows you to pre-render pages at build time.

The `getStaticPaths` function returns an array of paths that need to be pre-rendered.

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You can use the `getStaticPaths` function to pre-render pages for different languages.

By pre-rendering pages at build time, you can improve performance and reduce the load on your server.

However, pre-rendering pages at build time may also require more server resources.

To reduce the load on your server, you can use a technique called static site generation.

Static site generation is a technique that allows you to generate static HTML pages at build time.

Next.js provides a built-in function called `getStaticProps` that allows you to pre-render pages at build time.

The `getStaticProps` function returns an object with the pre-rendered page data.

You can use the `getStaticProps` function to pre-render pages for different languages.

By pre-rendering pages at build time, you can improve performance and reduce the load on your server.

However, pre-rendering pages at build time may also require more server resources.

To manage different languages and locales, you can use a technique called internationalization.

Internationalization is a technique that allows you to manage different languages and locales in a single application.

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Next.js provides a built-in function called `i18n` that allows you to manage different languages and locales.

The `i18n` function returns an object with information about the current locale.

You can use the `i18n` function to access the current locale and translation functions.

By using the `i18n` function, you can manage different languages and locales in a single application.

However, managing different languages and locales can also be complex and time-consuming.

To simplify the process, you can use a technique called localization.

Localization is a technique that allows you to manage different languages and locales in a single application.

Next.js provides a built-in function called `useTranslation` that allows you to manage different languages and locales.

The `useTranslation` function returns an object with two properties: `t` and `i18n`.

The `t` function is used to translate strings, while the `i18n` object provides information about the current locale.

You can use the `useTranslation` function to access the current locale and translation functions.

By using the `useTranslation` function, you can manage different languages and locales in a single application.

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However, using the `useTranslation` function can also be complex and time-consuming.

To simplify the process, you can use a technique called internationalization.

Internationalization is a technique that allows you to manage different languages and locales in a single application.

Next.js provides a built-in function called `i18n` that allows you to manage different languages and locales.

The `i18n` function returns an object with information about the current locale.

You can use the `i18n` function to access the current locale and translation functions.

By using the `i18n` function, you can manage different languages and locales in a single application.

However, managing different languages and locales can also be complex and time-consuming.

To simplify the process, you can use a technique called localization.

Localization is a technique that allows you to manage different languages and locales in a single application.

Next.js provides a built-in function called `useTranslation` that allows you to manage different languages and locales.

The `useTranslation` function returns an object with two properties: `t` and `i18n`.

The `t` function is used to translate strings, while the `i18n` object provides information about the current locale.

You can use the `useTranslation` function to access the

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Static Site Generation

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Static Site Generation is a powerful feature in Next.js that allows you to pre-render pages that don't have dynamic content or that change infrequently, speeding up initial page loads. This is especially useful for localized pages.

Next.js provides a built-in SSG function called getStaticPaths, which allows you to pre-render pages for each locale. To use this feature, you need to tell Next.js what locales to build the paths from, which you can do by defining your locales in next-i18next.config.js and passing them on to Next's next.config.js.

You can use Next.js's getStaticPaths function to create localized news details pages, for example. This involves creating a news article page for each of your configured supported locales, such as English (en) and Spanish (es).

To fetch the news item's localized details, you'll need to use the getStaticProps function, which will look like this: `getStaticProps({ params: { slug, locale } })`. This function will fetch the localized details from your mock backend.

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Using SSG can have some limitations, such as impacting build performance if you specify every supported locale. It's often more efficient to specify only the default locale and dynamically generate others as needed.

Here are some key takeaways to keep in mind when using SSG:

  • Use `generateStaticParams` to specify every supported locale, but be aware of the potential performance impact.
  • Use `getStaticPaths` to pre-render pages for each locale.
  • Use `getStaticProps` to fetch localized details for each page.
  • Be mindful of the limitations of statically exporting your site with next-intl.

Understanding Dates and Times

next-intl provides two main ways of formatting dates and times: standalone and in messages.

Date formatting varies across regions, with the United States using MM/DD/YYYY and many European countries using DD/MM/YYYY.

The format.dateTime function is locale-aware, and will format its given Date object per the rules of the active locale.

You can embed dates in your translation messages using the ICU {variable, date [, ::skeleton]} syntax. The ::EEEE ICU datetime skeleton displays the date as a long weekday, for example, "Thursday".

If you call the useFormatter hook within an async component, you'll get an error, so use the async getFormatter instead.

Here are some key things to know about dates and times in next-intl:

  • The English format does not show the full day of the week, but the short version instead (e.g. "Mon"). This can be worked around by using a custom global format.
  • By default, the server's time zone is used when formatting dates.
  • next-intl provides options for formatting relative times and date ranges.

Message Interpolation

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Message interpolation is a powerful feature in next-i18n that allows you to inject runtime values into your translation messages. You can use the {variable} interpolation syntax to do this.

For example, let's say you want to add a mock user greeting to your home page. You can use the {variable} syntax to inject the user's name into the translation message. This is demonstrated in Example 2, where it's shown that you can have as many {variable}s in your message as you desire, as long as you have an equivalent {variable: "Value"} in the second param passed to t() or your message won't render correctly.

By using message interpolation, you can create more dynamic and personalized translations that are tailored to each user's needs. This is particularly useful for applications that require a high degree of localization and personalization.

To use message interpolation, you need to specify an alternative localeStructure setting that matches your custom prefix and suffix. For example, if you want to use { and } as your prefix and suffix, your config would look like this:

How to Count Numbers

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Counting numbers can be a challenge when working with localized messages. In some regions, numbers are represented differently, such as in Tamil, where the Tamil numeral system (௦, ௧, ௨, ௩) is used.

To format numbers correctly, use the format.number() function, which is provided by next-intl. This function uses the Intl.NumberFormat standard to format numbers, and it passes any options in the second parameter to Intl.NumberFormat.

next-intl also allows you to embed numbers in translation messages using ICU skeletons. These skeletons start with :: and provide a way to format numbers with a specific pattern, such as ::precision-integer, which rounds the number to the nearest whole number.

ICU skeletons offer a lot of convenience and flexibility. Prebuilt skeletons like ::currency/USD or ::percent will use appropriate formatting for the active locale. You can also define global custom formats for reuse across your app.

To ensure that your numbers are formatted correctly, use region-specific locale codes, such as en-us, rather than en. This will help you avoid using Western Arabic numerals when they are not appropriate for the region.

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Here are some examples of ICU skeletons:

  • ::precision-integer (rounds the number to the nearest whole number)
  • ::currency/USD (uses appropriate formatting for the active locale)
  • ::percent (uses appropriate formatting for the active locale)
  • ::.##/@##r (formats a number with at most 2 fraction digits, but guarantees at least 3 significant digits)

Remember to test out the skeletons to ensure they work, as not all ICU skeletons work with next-intl.

Working with Dynamic Values in Messages

You can inject runtime values into a translation message using the {variable} interpolation syntax. This allows you to create dynamic content that changes based on user input or other factors.

To use this syntax, you simply place the variable name inside curly brackets within the translation message. For example, if you have a message like "Hello, {name}!", you can pass a value for the "name" variable when calling the translation function.

The translation function will then replace the {name} placeholder with the actual value, resulting in a message like "Hello, John!". This makes it easy to create personalized messages that are tailored to the user's needs.

Here's an example of how you might use this syntax in a real-world scenario:

  • "Welcome to our website, {username}!"
  • "You have {count} unread messages."
  • "The weather forecast for {city} is sunny."

By using the {variable} interpolation syntax, you can create dynamic messages that are more engaging and relevant to your users.

Page Metadata

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Page metadata is a crucial aspect of making your website accessible to a global audience. To localize page metadata, you'll need to use Next.js' async generateMetadata function.

You'll also need to utilize next-intl's async getTranslator function to fetch the translated messages. This is because metadata is managed outside of component rendering.

To demonstrate, let's localize our layout's metadata. First, we'll need to define the messages for each locale.

Now we can use these messages to localize our layout's metadata. We can see our site's title and description translated to the active locale.

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Type Safety and Dependencies

You'll need to install the right dependencies to get started with internationalization in Next.js. $ npm install i18next react-i18next i18next-resources-to-backend next-i18n-router is the command to install the required packages.

react-i18next and i18next are the core libraries for internationalization, and i18next-resources-to-backend helps with loading translations server-side. next-i18n-router is a lightweight package for internationalized routing and locale detection.

To implement internationalized routing and locale detection, you'll need to install next-i18n-router. It's a recommended resource in Next's App Router docs.

Declaring locale dependencies is crucial for certain use cases. By default, next-i18next sends only the active locale down to the client on each request.

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Fallback and Automatic Detection

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Fallback locales can be set to default to a specific language, and can be configured to support all variants of a language without the need for separate JSON files. This can increase the initial size of the page.

By default, next-i18next adds the defaultLocale as a fallback, but this can be changed by setting fallbackLng. All values supported by i18next, including strings, arrays, objects, and functions, are supported by next-i18next.

Automatic locale detection is a handy feature that enables us to easily identify the user's preferred language from the Accept-Language header. This feature is not only related to web apps but is also used in other areas like mobile app development.

To perform automatic locale detection, we can use the Negotiator library to extract the user's preferred languages from the Accept-Language header. This will route to the appropriate page variant.

Automatic locale detection will only be performed when a user visits the app's homepage for the first time. To test this feature for other app languages, we need to clear the NEXT_LOCALE cookie first.

If we want to disable automatic locale detection, we can set localeDetection to false in the next.config.js file. This will prevent Next.js from automatically redirecting based on the user's preferred locale.

Frequently Asked Questions

How does Next.js detect locales?

Next.js detects locales by analyzing the user's preferred language from the Accept-Language header and the current domain. This automatic locale detection helps tailor the application to the user's language preferences.

Jennie Bechtelar

Senior Writer

Jennie Bechtelar is a seasoned writer with a passion for crafting informative and engaging content. With a keen eye for detail and a knack for distilling complex concepts into accessible language, Jennie has established herself as a go-to expert in the fields of important and industry-specific topics. Her writing portfolio showcases a depth of knowledge and expertise in standards and best practices, with a focus on helping readers navigate the intricacies of their chosen fields.

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