Table of Contents
- TL;DR Source and Demo
- Introduction
- Project Setup
- Internationalized Routing
- Content translation
- Built-in Formatting
- Fetching from backend
TL;DR
Introduction
Internationalization (i18n) is the process of preparing software so that it can support local languages and cultural settings. An internationalized product supports the requirements of local markets around the world, functioning more appropriately based on local norms and better meeting in-country user expectations. Copy-pasted from here
In my early days of development, I find i18n to be a tedious task. However, in NextJS, it is relatively simple to create such as challenging feature.
Project Setup
Initialize a NextJS project
Let's start by creating a new NextJS project. The simplest way is to use these commands:
npx create-next-app@latest
# or
yarn create next-app
For more information, check this Create Next App docs
Remove boilerplate code
Let's simplify the project by removing unused code.
// pages/index.jsx
export default function Home() {
return <main>Hello world</main>;
}
Check the changes here
Create another route/page
This step is not related to i18n. It is mainly for easy demonstration.
Update the Home page to display the current locale.
// pages/index.jsx
import { useRouter } from "next/router";
export default function Home() {
const { locale } = useRouter();
return <main>Hello world: {locale}</main>;
}
Let's create an About page with the same content as the Home page.
// pages/about.jsx
import { useRouter } from "next/router";
export default function About() {
const { locale } = useRouter();
return <main>About page: {locale}</main>;
}
Without any configuration changes, the pages will be rendered as:
As you can see, localhost:3000
shows Hello world:
. This is because useRouter
is not aware of the value of locale
.
localhost:3000/zh-CN
and localhost:3000/sv
obviously will not exist because we have not created pages/zh-CN.jsx
and pages/sv.jsx
Internationalized Routing
Built-in NextJS i18n routing
Let's add this simple i18n
configuration to our next.config.js
file and see what happens.
// next.config.js
const nextConfig = {
// other stuff
i18n: {
defaultLocale: "en",
locales: ["en", "sv", "zh-CN"],
},
};
With the configuration above, we automagically get the locale
value and the following routes:
Home page
About page
Not defined locale
If you try to access localhost:3000/fr
, you will still get a 404 error. This is because we did not add fr
to our locale
values
Create a header component
To further simplify our demo, let's create a header component that can:
- Navigate to home and about pages
- Change the locale values using a dropdown
// components/Header.jsx
import React from "react";
import Link from "next/link";
import { useRouter } from "next/router";
const Header = () => {
const router = useRouter();
const handleLocaleChange = (event) => {
const value = event.target.value;
router.push(router.route, router.asPath, {
locale: value,
});
};
return (
<header>
<nav>
<Link href="/">
<a className={router.asPath === "/" ? "active" : ""}>Home</a>
</Link>
<Link href="/about">
<a className={router.asPath === "/about" ? "active" : ""}>About</a>
</Link>
</nav>
<select onChange={handleLocaleChange} value={router.locale}>
<option value="en">๐บ๐ธ English</option>
<option value="zh-CN">๐จ๐ณ ไธญๆ</option>
<option value="sv">๐ธ๐ช Swedish</option>
</select>
<style jsx>{`
a {
margin-right: 0.5rem;
}
a.active {
color: blue;
}
nav {
margin-bottom: 0.5rem;
}
`}</style>
</header>
);
};
export default Header;
Let's add the Header
component to our pages/_app.js
file.
// pages/_app.jsx
import Header from "../components/Header";
import "../styles/globals.css";
function MyApp({ Component, pageProps }) {
return (
<>
<Header />
<Component {...pageProps} />
</>
);
}
export default MyApp;
Now we can see clearly the power of NextJS built-in i18n support. We can now access the locale
value in our useRouter
hook, and the URL is updated based on the locale
.
To learn more about NextJS i18n routing, check this link.
Content translation
Unfortunately, there is no NextJS built-in support for content translation so we need to do it on our own.
However, there are a libraries that can help to not reinvent the wheel. In this blog post, we will use next-i18next.
Let's support content translation by setting up next-i18next
in our app.
Install next-i18next
npm install next-i18next
Create a next-i18next.config.js
and update next.config.js
// next-i18next.config.js
module.exports = {
i18n: {
defaultLocale: "en",
locales: ["en", "sv", "zh-CN"],
localePath: "./locales",
},
};
localePath
is optional and will default to ./public/locales
.
// next.config.js
const { i18n } = require("./next-i18next.config");
const nextConfig = {
// other stuff
i18n,
};
module.exports = nextConfig;
Create translation files
.
โโโ locales
โโโ en
| โโโ common.json
| โโโ home.json
โโโ zh-CH
| โโโ common.json
| โโโ home.json
โโโ se
โโโ common.json
โโโ home.json
English Translations
// locales/en/common.json
{
"greeting": "Hello world!"
}
// locales/en/home.json
{
"home": "Home",
"about": "About"
}
Please forgive me for any translation mistakes. I only used Google Translate to translate the content. ๐คฃ
Chinese translations
// locales/zh-CN/common.json
{
"greeting": "ไธ็ๆจๅฅฝ"
}
// locales/zh-CN/home.json
{
"home": "ไธป้กต",
"about": "ๅ
ณไบ้กต้ข"
}
Swedish translations
// locales/sv/common.json
{
"greeting": "Hej vรคrlden!"
}
// locales/sv/home.json
{
"home": "Hem",
"about": "Om"
}
There are three functions that
next-i18next
exports, which you will need to use to translate your project:
appWithTranslation
This is a HOC which wraps your _app
. This HOC is primarily responsible for adding a I18nextProvider.
// pages/_app.jsx
import { appWithTranslation } from "next-i18next";
import Header from "../components/Header";
import "../styles/globals.css";
function MyApp({ Component, pageProps }) {
return (
<>
<Header />
<Component {...pageProps} />
</>
);
}
export default appWithTranslation(MyApp);
serverSideTranslations
This is an async function that you need to include on your page-level components, via either getStaticProps or getServerSideProps.
// pages/index.jsx
import { serverSideTranslations } from "next-i18next/serverSideTranslations";
// export default function Home...
export async function getStaticProps({ locale }) {
return {
props: {
...(await serverSideTranslations(locale, ["common", "home"])),
// Will be passed to the page component as props
},
};
}
useTranslation
This is the hook which you'll actually use to do the translation itself. The useTranslation hook comes from react-i18next, but can be imported from next-i18next directly:
// pages/index.jsx
// other imports
import { useTranslation } from "next-i18next";
export default function Home() {
// We want to get the translations from `home.json`
const { t } = useTranslation("home");
// Get the translation for `greeting` key
return <main>{t("greeting")}</main>;
}
// export async function getStaticProps...
Let's also translate the links in the Header
component.
// components/Header.jsx
// other imports
import { useTranslation } from "next-i18next";
const Header = () => {
// ...
// If no argument is passed, it will use `common.json`
const { t } = useTranslation();
return (
<header>
<nav>
<Link href="/">
<a className={router.asPath === "/" ? "active" : ""}>{t("home")}</a>
</Link>
<Link href="/about">
<a className={router.asPath === "/about" ? "active" : ""}>
{t("about")}
</a>
</Link>
</nav>
{/* Other code */}
</header>
);
}
The changes above will yield the following output:
The home
page is translated properly; however, the about
page is not. It is because we need to use serverSideTranslations
in every route.
// pages/about.jsx
// other imports
import { serverSideTranslations } from "next-i18next/serverSideTranslations";
// export default function About...
export async function getStaticProps({ locale }) {
return {
props: {
...(await serverSideTranslations(locale, ["common"])),
},
};
}
Now both routes are translated
We only specified common
in the serverSideTranslations
because we don't plan on using anything in home.json
in the About page.
I will fetch the translations of the About page's content from the backend. But before that, let's first check some cool stuff we can do with our translation library.
Nested translation keys and default translation
We are not limited to a flat JSON structure.
// locales/en/newsletter.json
{
"title": "Stay up to date",
"subtitle": "Subscribe to my newsletter",
"form": {
"firstName": "First name",
"email": "E-mail",
"action": {
"signUp": "Sign Up",
"cancel": "Cancel"
}
}
}
We can omit some translation keys if we want it to use the default locale value(en
in our case).
// locales/zh-CN/newsletter.json
{
"title": "ไฟๆๆๆฐ็ถๆ",
"form": {
"email": "็ตๅญ้ฎ็ฎฑ",
"action": {
"cancel": "ๅๆถ"
}
}
}
Let's create a component which use the translations above.
// components/SubscribeForm.jsx
import { useTranslation } from "next-i18next";
import React from "react";
const SubscribeForm = () => {
const { t } = useTranslation("newsletter");
return (
<section>
<h3>{t("title")}</h3>
<h4>{t("subtitle")}</h4>
<form>
<input placeholder={t("form.firstName")} />
<input placeholder={t("form.email")} />
<button>{t("form.action.signUp")}</button>
<button>{t("form.action.cancel")}</button>
</form>
{/* For styling only */}
<style jsx>{`
form {
max-width: 300px;
display: flex;
flex-direction: column;
}
input {
margin-bottom: 0.5rem;
}
`}</style>
</section>
);
};
export default SubscribeForm;
Render the form in pages/index.jsx
and add newsletter
in serverSideTranslations
.
// pages/index.jsx
import { serverSideTranslations } from "next-i18next/serverSideTranslations";
import { useTranslation } from "next-i18next";
import SubscribeForm from "../components/SubscribeForm";
export default function Home() {
const { t } = useTranslation("home");
return (
<main>
<div>{t("greeting")}</div>
{/* Render the form here */}
<SubscribeForm />
</main>
);
}
export async function getStaticProps({ locale }) {
return {
props: {
...(await serverSideTranslations(locale, [
"common",
"home",
"newsletter", // Add newsletter translations
])),
},
};
}
Built-in Formatting
It is very easy to format most of our data since next-i18next
is using i18next under the hood.
Let's use the translation files below to showcase the formatting features.
// locales/en/built-in-demo.json
{
"number": "Number: {{val, number}}",
"currency": "Currency: {{val, currency}}",
"dateTime": "Date/Time: {{val, datetime}}",
"relativeTime": "Relative Time: {{val, relativetime}}",
"list": "List: {{val, list}}",
"weekdays": ["Monday", "Tuesday", "Wednesday", "Thursday", "Friday"]
}
// locales/zh-CN/built-in-demo.json
{
"number": "ๆฐ: {{val, number}}",
"currency": "่ดงๅธ: {{val, currency}}",
"dateTime": "ๆฅๆ/ๆถ้ด: {{val, datetime}}",
"relativeTime": "็ธๅฏนๆถ้ด: {{val, relativetime}}",
"list": "ๅ่กจ: {{val, list}}",
"weekdays": ["ๆๆไธ", "ๆๆไบ", "ๆๆไธ", "ๆๆๅ", "ๆๆไบ"]
}
// locales/sv/built-in-demo.json
{
"number": "Nummer: {{val, number}}",
"currency": "Valuta: {{val, currency}}",
"dateTime": "Datum/tid: {{val, datetime}}",
"relativeTime": "Relativ tid: {{val, relativetime}}",
"list": "Lista: {{val, list}}",
"weekdays": ["Mรฅndag", "Tisdag", "Onsdag", "Torsdag", "Fredag"]
}
Let's create a component which use the translations above.
import { useTranslation } from "next-i18next";
import React from "react";
const BuiltInFormatsDemo = () => {
const { t } = useTranslation("built-in-demo");
return (
<div>
<p>
{/* "number": "Number: {{val, number}}", */}
{t("number", {
val: 123456789.0123,
})}
</p>
<p>
{/* "currency": "Currency: {{val, currency}}", */}
{t("currency", {
val: 123456789.0123,
style: "currency",
currency: "USD",
})}
</p>
<p>
{/* "dateTime": "Date/Time: {{val, datetime}}", */}
{t("dateTime", {
val: new Date(1234567890123),
formatParams: {
val: {
weekday: "long",
year: "numeric",
month: "long",
day: "numeric",
},
},
})}
</p>
<p>
{/* "relativeTime": "Relative Time: {{val, relativetime}}", */}
{t("relativeTime", {
val: 12,
style: "long",
})}
</p>
<p>
{/* "list": "List: {{val, list}}", */}
{t("list", {
// https://www.i18next.com/translation-function/objects-and-arrays#objects
// Check the link for more details on `returnObjects`
val: t("weekdays", { returnObjects: true }),
})}
</p>
</div>
);
};
export default BuiltInFormatsDemo;
The more you look, the more you'll be amazed
Other translation functions to check
Fetching translations from backend
The work here is mainly done on the backend side or your CMS. On the frontend, we simply fetch the translations and pass a parameter to distinguish the language we want.
I created a simple endpoint to fetch the content of the about page. The result will change based on query param lang
value.
// pages/api/about.js
export default function handler(req, res) {
const lang = req.query.lang || "en";
if (lang === "sv") {
return res.status(200).json({ message: "Jag รคr Code Gino" });
} else if (lang === "zh-CN") {
return res.status(200).json({ message: "ๆๆฏไปฃ็ ๅ่ฏบ" });
} else {
return res.status(200).json({ message: "I am Code Gino" });
}
}
Sample usage
-
/api/about
: English -
/api/about?lang=zh-CN
: Simplified Chinese -
/api/about?lang=sv
: Svenska -
/api/about?lang=invalid
: English
We can consume the API as usual (e.g. inside getServerSideProps
, getStaticProps
, useEffect
, etc.).
In this example, let's fetch the translation inside the getStaticProps
. We can get the locale
value from the context, then append ?lang=${locale}
to our request URL.
// pages/about.jsx
// This import is not related to fetching translations from backend.
import { serverSideTranslations } from "next-i18next/serverSideTranslations";
export default function About({ message }) {
return <h1>{message}</h1>;
}
export async function getStaticProps({ locale }) {
const { message } = await fetch(
// forward the locale value to the server via query params
`https://next-i18n-example-cg.vercel.app/api/about?lang=${locale}`
).then((res) => res.json());
return {
props: {
message,
// The code below is not related to fetching translations from backend.
...(await serverSideTranslations(locale, ["common"])),
},
};
}
The code above will yield the following result:
Conclusion
Internationalization is a complex requirement simplified in Next.js due to the built-in i18n routing support and the easy integration of next-i18next. And because next-i18next
is using i18next
, we can perform better translations with less code.
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