Internationalization i18n in Node.js: i18next

Internationalization (i18n) in JavaScript (Node.js): i18next Library

Internationalization (abbreviated as i18n — from the English "internationalization", where 18 is the number of letters between the first "i" and the last "n") is the process of designing and developing software that allows it to be adapted to different languages and regional features without changing the source code. In modern web development on Node.js, creating multilingual applications is a necessity for entering the global market.

One of the most popular and powerful libraries for implementing i18n in the JavaScript ecosystem (including Node.js) is i18next. It offers a flexible architecture, support for multiple translation file formats, interpolation, pluralization, and contextual translations. In this article, we will thoroughly cover the installation, configuration, and use of i18next on the server side.

Installation and Setup

To start working with i18next in a Node.js project, install the library via npm:

npm install i18next

It is also recommended to install the i18next-fs-backend package for loading translation files from the file system:

npm install i18next-fs-backend

After installation, create an initialization file, for example i18n.js:

const i18next = require('i18next');const Backend = require('i18next-fs-backend');

i18next.use(Backend).init({  lng: 'ru', // default language  fallbackLng: 'en', // fallback language  backend: {    loadPath: './locales/{{lng}}/{{ns}}.json' // path to translation files  },  interpolation: {    escapeValue: false // do not escape HTML (for Node.js)  }});

module.exports = i18next;

Translation File Structure

Create a locales folder in the project root. Inside it, create a subfolder for each language (e.g., en, ru, de). In each subfolder, place JSON files with translations. Typically, one translation.json file is used per language, but you can split them into namespaces for modularity.

Example of the file locales/ru/translation.json:

{  "welcome": "Добро пожаловать на наш сайт!",  "greeting": "Привет, {{name}}!",  "items": "{{count}} элемент",  "items_plural": "{{count}} элементов",  "menu": {    "home": "Главная",    "about": "О нас",    "contact": "Контакты"  }}

Example of the file locales/en/translation.json:

{  "welcome": "Welcome to our website!",  "greeting": "Hello, {{name}}!",  "items": "{{count}} item",  "items_plural": "{{count}} items",  "menu": {    "home": "Home",    "about": "About",    "contact": "Contact"  }}

Main Features of i18next

Simple Translation

To get a translation, use the t() function (from "translate"):

const i18next = require('./i18n');

// Asynchronous initialization (in a real project, wait for readiness)i18next.t('welcome'); // "Добро пожаловать на наш сайт!" (if lng: 'ru')

Variable Interpolation

Insert dynamic values into strings using double curly braces:

i18next.t('greeting', { name: 'Алексей' });// Result: "Привет, Алексей!"

Pluralization

The library automatically selects the correct plural form based on the language's rules. To do this, add keys with the _plural suffix:

i18next.t('items', { count: 1 }); // "1 элемент"i18next.t('items', { count: 5 }); // "5 элементов"

For English, the rule is simpler (one item — item, many — items). For Russian, i18next uses built-in pluralization rules that account for numbers 1, 2-4, 5-20, etc.