next-locales

Internationalization support for Next.js with static HTML export.

Installation

To install the library simply add the module.
You can use npm:

npm i next-locales

or i.e. Yarn if you prefer:

yarn add next-locales

Configuration

Create a file in the root path of your Next.js project called: .i18nrc.json.
This file stores the basic configuration needed for this library to run.

{
  "localesDir": "./src/locales",
  "locales": ["en", "pl"],
  "defaultLocale": "en"
}

In the next step, edit your next.config.js file, importing in it high order function withLocalesConfig from this library.

Let it look something like this:

const { withLocalesConfig } = require('next-locales/server');

module.exports = withLocalesConfig({
  // your custom Next.js config
});

Pages integration

Now we will go to the pages directory. You may be using the src directory, then the path might look like this: src/pages. Here are all the pages on which Next.js works.

In this directory, edit the _app.jsx or _app.tsx file (if your project uses TypeScript). If such a file does not exist in your project, create it.

This is how it should look like in the simplest form:

import { AppProps as CustomAppProps } from 'next/app';
import { withLocales } from 'next-locales';

const CustomApp = ({ Component, pageProps }: CustomAppProps) => (
  <Component {...pageProps} />
);

export default withLocales(CustomApp);

Moving pages (Important!)

Now it's time to create a directory inside pages or src/pages.
Such directory must be named [locale].

Next, move all files and directories except for files such as: _app.jsx, _document.jsx, _error.jsx, 404.jsx or 500.jsx (or .tsx in the TypeScript case) that you previously had in the pages directory to this created directory.

The index.jsx file (for the home page) should also be moved.

New index.jsx page

Since your home page has been moved to the new [locale] directory, you should create a new file index.jsx with the content as below:

import { createInitialIndexPage } from 'next-locales';

export default createInitialIndexPage();

This is needed to properly export the Next.js project with this library.

Translation files

You translation files should be located at localesDir set in the .i18nrc file. This library supports two types of translations that you can use - JSON and Yaml.

Each language added to the locales configuration array should have its file here with the same name. For example, pl.json and en.json (pl.yml and en.yml if you prefer Yaml).

Example of Yaml translations

en.yml

testing:
  welcome: Hello {{ name }}!
  userinfo:
    age: Age
    gender: Gender

pl.yml

testing:
  welcome: Cześć {{ name }}!
  userinfo:
    age: Wiek
    gender: Płeć

As you can see above - you can use placeholders.
This library implements Mustache template system (https://github.com/janl/mustache.js) which enables this functionality.

Using translation in components

For translations to work, you need to import high order functions - withLocalesStaticProps and withLocalesStaticPaths in each file where you want to use translation.

import {
  withLocalesStaticProps,
  withLocalesStaticPaths,
} from 'next-locales/server';

const ExamplePage = () => <div>This is an example page</div>;

export const getStaticProps = withLocalesStaticProps();
export const getStaticPaths = withLocalesStaticPaths();

export default ExamplePage;

If you need a custom getStaticProps or getStaticPaths function, just pass the function as the first HOC parameter. Like that:

export const getStaticProps = withLocalesStaticProps(async ({ params }) => {
  const additionalProp = 'Hello World!';

  return {
    props: {
      additionalProp,
    },
  };
});

export const getStaticPaths = withLocalesStaticPaths(() => ({
  paths: ['/example', '/hello/world'],
  fallback: false,
}));

If the implementation of getStaticProps and getStaticPaths is fine - you are ready to use your translations!

All you need at this point is to use the useTranslation hook.

Full example:

import {
  withLocalesStaticProps,
  withLocalesStaticPaths,
} from 'next-locales/server';

const ExamplePage = () => {
  const { t } = useTranslation();

  return <div>{t('testing.welcome', { name: 'Guest' })}</div>;
};

export const getStaticProps = withLocalesStaticProps();
export const getStaticPaths = withLocalesStaticPaths();

export default ExamplePage;

The useTranslation hook returns the t function. It takes a translation key as the first parameter, and an object for replacing placeholders as the second optional parameter.

Support for links with the Link component

This library provides a modified Link component to be used for any links and redirects in the application. It provides support for locales.

import {
  withLocalesStaticProps,
  withLocalesStaticPaths,
} from 'next-locales/server';
import { Link } from 'next-locales';

const ExamplePage = () => <Link href="/example/page">Page</Link>;

export const getStaticProps = withLocalesStaticProps();
export const getStaticPaths = withLocalesStaticPaths();

export default ExamplePage;

Setting the lang attribute

To set the lang attribute for the <html> tag, create a custom document _document.jsx file and use the getLangAttrValue function:

import { Html, Head, Main, NextScript } from 'next/document';
import { getLangAttrValue } from 'next-locales/server';

const CustomDocument = ({ __NEXT_DATA__ }) => (
  <Html lang={getLangAttrValue(__NEXT_DATA__)}>
    <Head />
    <body>
      <Main />
      <NextScript />
    </body>
  </Html>
);

export default CustomDocument;

Setting the dir attribute for the locale

To set the dir attribute for the <html> tag, you need to add a special __config section in the translation file and provide a value for the dir field:

en.yml

__config:
  dir: rtl

The field value is validated. It currently takes the values ltr, rtl, and auto. The default is ltr.

The next step is to get the dir value for the currently active locale. You do this in a similar way as seen above, when setting the lang attribute but here you are using a slightly different function with the name getDirAttrValue:

import { Html, Head, Main, NextScript } from 'next/document';
import { getDirAttrValue } from 'next-locales/server';

const CustomDocument = ({ __NEXT_DATA__ }) => (
  <Html dir={getDirAttrValue(__NEXT_DATA__)}>
    <Head />
    <body>
      <Main />
      <NextScript />
    </body>
  </Html>
);

export default CustomDocument;

Setting the lang and dir attribute at once

This library also provides a util, with which you can get an object with the lang and dir fields with one function and insert it like this:

import { Html, Head, Main, NextScript } from 'next/document';
import { getHtmlLocaleAttributes } from 'next-locales/server';

const CustomDocument = ({ __NEXT_DATA__ }) => (
  <Html {...getHtmlLocaleAttributes(__NEXT_DATA__)}>
    <Head />
    <body>
      <Main />
      <NextScript />
    </body>
  </Html>
);

export default CustomDocument;

The use of this function may override the setting of the lang and dir attributes separately.

Acknowledgments

Thanks to Adriano Raiano (https://github.com/adrai) for sharing the library next-language-detector (https://github.com/adrai/next-language-detector) which is used in this project.