Implementing localization in software applications can be overwhelming, especially for complex applications that haven't been prepared for internationalization (i18n).

In this article, I’ll walk you through an easy and efficient approach to localization in a Next.js application using Tolgee - a platform designed for fast and autonomous translation management.

You will also see how to integrate Tolgee with complex Next.js project - Dub.co, a popular link management platform allowing users to access and interact with the application in their preferred languages.

Prerequisites

To fully understand this Article, you need to have a basic understanding of React or Next.js.

You will also need to set up the following if you would like to use this article as tutorial:

• Tolgee Project - an existing project with at least two language translations.

• Tolgee CLI - allows you to interact with the Tolgee platform from your computer using the command line.

• Docker - required for running Dub.co. It is an open-source platform that uses containerization to make it easier to create, deploy, and run applications.

• Docker Compose - a software application for defining and running multi-container Docker applications.

• Python (version 3.8 or higher): necessary for configuring some of Dub.co’s packages.

What is Tolgee?

Tolgee is a developer-friendly localization platform that allows you to translate your application into any language without modifying your code. It is designed for web applications but also supports mobile and desktop applications. With Tolgee, you don't need to look for keys in your source code, edit localization files, or perform manual exporting data for translators. Tolgee is a fast and painless platform that offers in-context translation, a translation memory for keeping track of already translated strings, machine and auto translations, and many others.

How to set up Dub.co on your local computer

Dub.co is an open-source link management platform that allows marketing teams to add powerful analytics to their links, create short links, generate QR codes for links, and many more. It was created by Steven Tey (formerly of Vercel).

Follow these steps to set up Dub.co on your computer:

Clone the Dub.co GitHub repository by running the code snippet below.

git clone https://github.com/dubinc/dub.git

Navigate into the dub folder and install the project dependencies:

pnpm install

Within the apps/web folder, rename the .env.example file to .env.

Create a new Tinybird account, and copy your Admin Auth Token into the .env file.

TINYBIRD_API_KEY=<your_admin_auth_token>

Navigate into the packages/tinybird directory and install the Tinybird CLI using the following command:

pip3 install tinybird-cli

Execute the following command in your terminal and enter your Admin Auth Token when prompted to authenticate using the Tinybird CLI:

tb auth

Publish the Tinybird datasource and endpoints by running the code snippet below:

tb push

Create an Upstash database and copy the following credentials from the REST API section to the .env file:

UPSTASH_REDIS_REST_URL=<your_rest_url>
UPSTASH_REDIS_REST_TOKEN=<your_rest_token>

Navigate to the QStash tab and copy the following credentials into the .env file.

QSTASH_TOKEN=
QSTASH_CURRENT_SIGNING_KEY=
QSTASH_NEXT_SIGNING_KEY

Next, within the apps/web directory, run the following command to start the Docker Compose stack:

docker-compose up

Generate the Prisma client and create its database tables using the following commands:

npx prisma generate
npx prisma db push

Dub.co supports multiple authentication methods. Create a GitHub app and copy the URL below as its callback URL.

http://localhost:8888/api/auth/callback/github

Finally, start the development server:

pnpm dev

You can access the web application by navigating to http://localhost:8888 in your browser, create a workspace, and get started. If you encounter any issues, refer to the complete installation guide for more detailed assistance.

How to configure Tolgee in a Next.js application

In this section, I'll show you how to add Tolgee to a Next.js application and configure it to support multiple languages, allowing users to access the app in their preferred language.

To implement localization in Next.js applications, you’ll need to install the Tolgee React SDK.

npm install @tolgee/react

Next, create a Tolgee Platform account and sign into your dashboard.

Add a new project by clicking the Project button and selecting your preferred languages for the project. For this application, we'll use five languages: English (as the base language), Chinese, Hindi, Spanish, and Arabic.

Click the profile icon in the top-right corner of your dashboard, then select Project API Keys to create an API key for your Tolgee project.

Create a .env.development.local and copy your API key into the file:

NEXT_PUBLIC_TOLGEE_API_KEY=<paste_your_API_key_here>

Select Translations from the sidebar menu and add a new translation to the project.

You can create a translation key, add the content or string you need to translate, provide a description, and then save it.

Tolgee provides various machine translation options by default, allowing you to easily translate content into the available languages within your project.

Congratulations! You’ve successfully set up the Tolgee platform for translations within your application. Next, let’s configure Tolgee within the Dub.co project to easily generate translations directly in the application.

How to set up localization in Dub.co

In this section, I’ll guide you through configuring Tolgee to support client-server interactions within the Dub.co project.

First, install the Tolgee CLI package.

npm install --global @tolgee/cli

Run the following code snippet to sign in to your Tolgee platform using your project API key.

tolgee login <your_tolgee_api_key

Next, create an i18n folder within the apps/web directory. This folder will store the JSON files containing translations for the various languages available in the Tolgee platform project.

apps
├── web #👈🏼 this folder
├── app
├── i18n #👈🏼 newly created
packages
├── tailwind-config
├── tinybird
├── tsconfig
├── ui
├── utils

Within the apps/web directory, fetch the language translations created in your Tolgee project by running the code snippet below:

tolgee --project-id <tolgee_platform_project_id> pull --path ./i18n

The code snippet above automatically populates the i18n folder with the various language translations created within the Tolgee platform.

apps
├── web
├── app
├── i18n #👇🏻 translation files
├── ar.json
├── en.json
├── es.json
├── zh.json
packages
├── tailwind-config
├── tinybird
├── tsconfig
├── ui
├── utils

Create a tolgee folder which will contain Tolgee configurations within the apps/web directory:

apps
├── web # 👈🏼 this folder
├── app
├── i18n
├── tolgee # 👈🏼 Tolgee folder
packages
├── tailwind-config
├── tinybird
├── tsconfig
├── ui
├── utils

Add a shared.ts file in the tolgee directory, then copy the following code snippet into the file:

import { FormatIcu } from "@tolgee/format-icu";
import { DevTools, Tolgee } from "@tolgee/react";

const apiKey = process.env.NEXT_PUBLIC_TOLGEE_API_KEY;
const apiUrl = process.env.NEXT_PUBLIC_TOLGEE_API_URL;

//👇🏻 available translations
export const ALL_LOCALES = ["en", "ar", "es", "zh"];

//👇🏻 default translation
export const DEFAULT_LOCALE = "en";

//👇🏻 returns an object containing the translation files
export async function getStaticData(languages: string[]) {
const result: Record<string, any> = {};

for (const lang of languages) {
result[lang] = (await import(`../i18n/${lang}.json`)).default;
}

return result;
}

export function TolgeeBase() {
return Tolgee().use(FormatIcu()).use(DevTools()).updateDefaults({
apiKey,
apiUrl,
fallbackLanguage: "en",
defaultLanguage: DEFAULT_LOCALE,
});
}

The code snippet above configures Tolgee with default and fallback languages to enable localization within the application.

Next, create a client.tsx file in the tolgee directory, then copy the code snippet below into the file:

'use client';

import { TolgeeBase } from './shared';
import { TolgeeProvider, useTolgeeSSR } from '@tolgee/react';
import { useRouter } from 'next/navigation';
import { useEffect } from 'react';

type Props = {
locales: any;
locale: string;
children: React.ReactNode;
};

const tolgee = TolgeeBase().init();

export const TolgeeNextProvider = ({ locale, locales, children }: Props) => {
const tolgeeSSR = useTolgeeSSR(tolgee, locale, locales);
const router = useRouter();

useEffect(() => {
const { unsubscribe } = tolgeeSSR.on('permanentChange', () => {
router.refresh();
});

return () => unsubscribe();
}, [tolgeeSSR, router]);

return (
<TolgeeProvider
tolgee={tolgeeSSR}
options={{ useSuspense: false }}
fallback="Loading"
>
{children}
</TolgeeProvider>
);
};

The client.tsx file serves the purpose of translating client components and also enables the in-context functionality for server-rendered components. The code snippet above defines the TolgeeNextProvider component, which wraps the entire Dub.co application, providing configurations needed to manage language changes and translations.

As mentioned earlier in the article, the Dub.co code repository includes custom routing configurations that conflict with Tolgee’s default Next.js integration guide. To resolve this, create a custom locale.ts file in the tolgee folder and copy the following code snippet into it:

"use server";

import { cookies, headers } from "next/headers";
import { ALL_LOCALES, DEFAULT_LOCALE } from "./shared.ts";

const COOKIE_NAME = "NEXT_LOCALE";

//👇🏻 Retrieves the current language setting for the user.
// If not set, it attempts to detect the user's language from browser preferences.
// Defaults to the application's default locale if no match is found.
export async function getUserLocale() {
return (
cookies().get(COOKIE_NAME)?.value || detectLanguage() || DEFAULT_LOCALE
);
}

//👇🏻 Sets the user’s preferred language in a cookie to persist their selection.
export async function setUserLocale(locale: string) {
cookies().set(COOKIE_NAME, locale);
}

//👇🏻 Attempts to detect the user's preferred language based on browser settings.
const detectLanguage = () => {
const allPreferred = getAcceptedLanguages();

for (const language of allPreferred) {
// Checks for an exact match in the list of supported locales
const exactMatch = ALL_LOCALES.find((l) => l === language);
if (exactMatch) {
return exactMatch;
}

// Falls back to matching only the two-letter language code
const getTwoLetters = (fullTag: string) =>
fullTag.replace(/^(.+?)(-.*)?$/, "$1");

const preferredTwoLetter = getTwoLetters(language);
const twoLetterMatch = ALL_LOCALES.find(
(l) => getTwoLetters(l) === preferredTwoLetter,
);
if (twoLetterMatch) {
return twoLetterMatch;
}
}
};

//👇🏻 Retrieves accepted languages from the "Accept-Language" HTTP header.
// Returns an array of languages in order of preference.
function getAcceptedLanguages() {
const acceptLanguageHeader = getAcceptLanguageHeader();
if (!acceptLanguageHeader) {
return [];
}

// Splits the header value by commas to separate each language code
return acceptLanguageHeader.split(",").map((lang) => {
const [language] = lang.split(";");
return language.trim();
});
}

//👇🏻 Fetches the "Accept-Language" HTTP header from the user's browser.
// This header lists languages preferred by the user, ranked by preference.
function getAcceptLanguageHeader() {
return headers().get("Accept-Language");
}

Finally, create a server.tsx file in the tolgee folder, then copy the following code snippet into the file:

import { getUserLocale } from "./locale.ts";
import { TolgeeBase, ALL_LOCALES, getStaticData } from './shared';
import { createServerInstance } from '@tolgee/react/server';

export const { getTolgee, getTranslate, T } = createServerInstance({
getLocale: async () => getUserLocale(),
createTolgee: async (locale) =>
TolgeeBase().init({
// including all locales
// on server we are not concerned about bundle size
staticData: await getStaticData(ALL_LOCALES),
observerOptions: {
fullKeyEncode: true,
},
language: locale,
fetch: async (input, init) => {
const data = await fetch(input, { ...init, next: { revalidate: 0 } });
return data;
},
}),
});

The application utilizes the React server cache for sharing Tolgee instance across components in a single render. This allows the app to use the Tolgee instance anywhere in the server components.

Congratulations! You’ve successfully configured Tolgee and are now ready to start adding translations to various content within the application.

How to translate your application content with Tolgee

Here, you'll learn how to translate content within your web application and see how Tolgee enables easy in-app translation.

To get started, you need to wrap the entire Dub.co application with the TolgeeNextProvider component, defined in tolgee/client.tsx. Navigate to the apps/web/app folder, then go to the app.dub.co/(dashboard) directory, and update the layout.tsx file as shown below:

import { MainNav } from "@/ui/layout/main-nav";
import { HelpButtonRSC } from "@/ui/layout/sidebar/help-button-rsc";
import Toolbar from "@/ui/layout/toolbar/toolbar";
import { constructMetadata } from "@dub/utils";
import { ReactNode } from "react";
import Providers from "../../providers";
//👇🏻 Tolgee imports
import { TolgeeNextProvider } from "../../../tolgee/client.tsx";
import { getUserLocale } from "../../../tolgee/locale.ts";
import { getStaticData } from "../../../tolgee/shared.ts";

export const metadata = constructMetadata();

export default async function Layout({ children }: { children: ReactNode }) {
const locale = await getUserLocale();
const locales = await getStaticData([locale, "en"]);

return (
<TolgeeNextProvider locale={locale} locales={locales}>
<Providers>
<div className="min-h-screen w-full bg-white">
<MainNav toolContent={<HelpButtonRSC />}>{children}</MainNav>
</div>
{/* <ChangelogPopup /> */}
<Toolbar show={["onboarding"]} />
</Providers>
</TolgeeNextProvider>
);
}

The code snippet above wraps the dashboard routes with the Tolgee provider, enabling language switching and localization throughout the application.

Tolgee provides two hooks to help you select and translate text within your application: useTolgee and useTranslate.

• The useTolgee hook returns the Tolgee instance, allowing you to subscribe to various events that will trigger re-renders when translating text.

• The useTranslate hook includes a translation function (t function) that renders the actual translations directly within the app.

Update the page.tsx file in the app.dub.co/(dashboard)/[slug] directory by adding the following code snippet:

"use client";
import { PageContent } from "@/ui/layout/page-content";
import WorkspaceLinksClient from "./page-client";
//👇🏻 Tolgee installations
import { useTolgee, useTranslate } from "@tolgee/react";
import { setUserLocale } from "tolgee/locale";

export default function WorkspaceLinks() {
const { t } = useTranslate();
const tolgee = useTolgee(["pendingLanguage"]);
const language = tolgee.getPendingLanguage();

return (
<PageContent title="Links">
{/** -- HTML input for selecting the preferred language -- */}
<div className="flex w-full flex-col px-10">
<p>Select Language</p>
<select
defaultValue={language}
className="rounded-sm"
name="locale"
id="locale"
onChange={(e) => setUserLocale(e.currentTarget.value)}
>
<option value="en">English</option>
<option value="es">Spanish</option>
<option value="ar">Arabic</option>
<option value="zh">Chinese</option>
</select>

<p>{t("hello")}</p>
</div>
{/** -- end of Tolgee -- */}
<WorkspaceLinksClient />
</PageContent>
);
}

The code snippet above displays an HTML <select> tag that allows users to choose and switch between different languages. The {t("hello")} element uses Tolgee’s translation function to render a value of the "hello" key based on the selected language.

Finally, you can update the remaining content throughout the application to support language changes, allowing users to view all components in their selected language.

We are currently working on AI migration agent, which will automatically convert your project files to be translated with Tolgee Native SDKs. You can check the repository here.

Tolgee also provides an in-context translation feature, allowing you to translate strings directly within your application, whether in development or production, simply by clicking the text and holding the Alt / Option key.

And that's it. This is how I integrated Tolgee to Dub.co.

The source after these changes is available here:

https://github.com/JanCizmar/dub-with-tolgee

Next Steps

So far, you’ve learned how to add localization to your software applications using Tolgee, implement support for multiple languages, and make language switching seamless within a real-world project.

Tolgee is a fast, developer-focused localization platform that allows you to provide context to your content and generate translations in seconds. It also supports multiple JavaScript frameworks, including Vue, Angular, and Svelte, and integrates with tools like Figma and a REST API for flexibility.

If you're looking to create a personalized experience for your users, Tolgee is an excellent choice. Feel free to contribute and star our GitHub repository, and join our Slack community to connect with others and engage with the team.

Thank you for reading!