nestjs-i18n

What is nestjs-i18n?

nestjs-i18n is a powerful internationalization (i18n) module for NestJS applications. It provides a comprehensive set of tools to manage translations, handle localization, and support multiple languages in a NestJS application.

What are nestjs-i18n's main functionalities?

Basic Setup

This code sets up the basic configuration for nestjs-i18n. It initializes the I18nModule with a fallback language and specifies the parser and the path to the translation files.

```typescript
import { Module } from '@nestjs/common';
import { I18nModule, I18nJsonParser } from 'nestjs-i18n';
import * as path from 'path';

@Module({
  imports: [
    I18nModule.forRoot({
      fallbackLanguage: 'en',
      parser: I18nJsonParser,
      parserOptions: {
        path: path.join(__dirname, '/i18n/'),
      },
    }),
  ],
})
export class AppModule {}
```

Translation Service

This code demonstrates how to use the I18nService to translate a message. The `translate` method is used to fetch the translation for the given key ('HELLO_MESSAGE').

```typescript
import { Injectable } from '@nestjs/common';
import { I18nService } from 'nestjs-i18n';

@Injectable()
export class AppService {
  constructor(private readonly i18n: I18nService) {}

  async getHello(): Promise<string> {
    return this.i18n.translate('HELLO_MESSAGE');
  }
}
```

Request Scoped Translations

This code shows how to use request-scoped translations. By injecting the I18nContext into the controller method, you can translate messages based on the current request's language.

```typescript
import { Controller, Get } from '@nestjs/common';
import { I18n, I18nContext } from 'nestjs-i18n';

@Controller()
export class AppController {
  @Get()
  async getHello(@I18n() i18n: I18nContext): Promise<string> {
    return i18n.translate('HELLO_MESSAGE');
  }
}
```

Other packages similar to nestjs-i18n

i18next

i18next is a popular internationalization framework for JavaScript applications. It provides a wide range of features for managing translations and supports various backends for loading translation files. Compared to nestjs-i18n, i18next is more general-purpose and can be used with any JavaScript framework, not just NestJS.

nestjs-i18n

nestjs-i18n is another internationalization module for NestJS. It offers similar functionalities to nestjs-i18n, such as managing translations and supporting multiple languages. However, it may have different configuration options and features.

react-i18next

react-i18next is a powerful internationalization library specifically designed for React applications. It builds on top of i18next and provides React-specific bindings. While it offers similar translation management features, it is tailored for use with React rather than NestJS.

README

Description

The i18n module for Nest.

Installation

$ npm i --save nestjs-i18n

Quick Start

Structure

create a directory and in it define your language keys as directories.

i18n
├── en
│   ├── category.json
│   └── auth.json
└── nl
    ├── category.json
    └── auth.json

Translation File

The format of a translation file could look like this:

{
  "HELLO_MESSAGE": "Hello {username}",
  "GOODBYE_MESSAGE": "Goodbye {username}",
  "USER_ADDED_PRODUCT": "{0.username} added {1.productName} to cart",
  "SETUP": {
    "WELCOME": "Welcome {0.username}",
    "GOODBYE": "Goodbye {0.username}"
  },
  "ARRAY": ["ONE", "TWO", "THREE"]
}

String formatting is done by: string-format

Translation Module

To use the translation service we first add the module. The I18nModule has a @Global() attribute so you should only import it once.

import { Module } from '@nestjs/common';
import * as path from 'path';
import { I18nModule } from 'nestjs-i18n';

@Module({
  imports: [
    I18nModule.forRoot({
      path: path.join(__dirname, '/i18n'),
      filePattern: '*.json',
      fallbackLanguage: 'en',
    }),
  ],
  controllers: [],
})
export class AppModule {}

Using forRootAsync()

import { Module } from '@nestjs/common';
import * as path from 'path';
import { I18nModule } from 'nestjs-i18n';

@Module({
  imports: [
    I18nModule.forRootAsync({
      useFactory: (configService: ConfigurationService) => ({
        path: configService.i18nPath,
        fallbackLanguage: configService.fallbackLanguage, // e.g., 'en'
        filePattern: configService.i18nFilePattern, // e.g., '*.i18n.json'
      }),
      inject: [ConfigurationService],
    }),
  ],
  controllers: [],
})
export class AppModule {}

Language Resolvers

To make it easier to manage in what language to respond you can make use of resolvers

@Module({
  imports: [
    I18nModule.forRoot({
      path: path.join(__dirname, '/i18n/'),
      fallbackLanguage: 'en',
      resolvers: [
        { use: QueryResolver, options: ['lang', 'locale', 'l'] },
        HeaderResolver,
        new CookieResolver(['lang', 'locale', 'l']),
      ],
    }),
  ],
  controllers: [HelloController],
})
export class AppModule {}

Currently, there are two built-in resolvers

Resolver	Default value
QueryResolver	none
HeaderResolver	accept-language
CookieResolver	lang

To implement your own resolver (or custom logic) use the I18nResolver interface. The resolvers are provided via the nestjs dependency injection, this way you can inject your own services if needed.

@Injectable()
export class QueryResolver implements I18nResolver {
  constructor(@I18nResolverOptions() private keys: string[]) {}

  resolve(req: any) {
    let lang: string;

    for (const key of this.keys) {
      if (req.query != undefined && req.query[key] !== undefined) {
        lang = req.query[key];
        break;
      }
    }

    return lang;
  }
}

To provide initial options to your custom resolver use the @I18nResolverOptions() decorator, also provide the resolver as followed:

I18nModule.forRoot({
  path: path.join(__dirname, '/i18n/'),
  fallbackLanguage: 'en',
  saveMissing: false,
  resolvers: [{ use: QueryResolver, options: ['lang', 'locale', 'l'] }],
});

Using forRootAsync()

I18nModule.forRootAsync({
  useFactory: () => {
    return {
      path: path.join(__dirname, '/i18n'),
      fallbackLanguage: 'en',
      saveMissing: false,
    };
  },
  resolvers: [{ use: QueryResolver, options: ['lang', 'locale', 'l'] }],
});

Translating with i18n module

I18nLang decorator and I18nService

@Controller()
export class SampleController {
  constructor(private readonly i18n: I18nService) {}

  @Get()
  sample(@I18nLang() lang: string) {
    this.i18n.translate('HELLO_MESSAGE', {
      lang: lang,
      args: { id: 1, username: 'Toon' },
    });
    this.i18n.translate('SETUP.WELCOME', {
      lang: 'en',
      args: { id: 1, username: 'Toon' },
    });
    this.i18n.translate('ARRAY.0', { lang: 'en' });
  }
}

I18n decorator

@Controller()
export class SampleController {
  @Get()
  sample(@I18n() i18n: I18nContext) {
    i18n.translate('HELLO_MESSAGE', { args: { id: 1, username: 'Toon' } });
    i18n.translate('SETUP.WELCOME', { args: { id: 1, username: 'Toon' } });
    i18n.translate('ARRAY.0');
  }
}

No need to handle lang manually.

I18nRequestScopeService within a custom service using request scoped translation service

@Injectable()
export class SampleService {
  constructor(private readonly i18n: I18nRequestScopeService) {}

  doFancyStuff() {
    this.i18n.translate('HELLO_MESSAGE', { args: { id: 1, username: 'Toon' } });
    this.i18n.translate('SETUP.WELCOME', { args: { id: 1, username: 'Toon' } });
    this.i18n.translate('ARRAY.0');
  }
}

To be used within other services like sending E-mails. The advantage is that you don't have to worry about transporting lang from the Request to your service.

Use with caution! The I18nRequestScopeService uses the REQUEST scope and is no singleton. This will be inherited to all consumers of I18nRequestScopeService! Read Nest Docs for more information.

Dont use I18nRequestScopeService within controllers. The I18n decorator is a much better solution.

Missing Translations

If you require a translation that is missing, I18n will log an error. However, you can also write these missing translations to a new file in order to help translating your application later on.

This behaviour can be controlled via the saveMissing: boolean attribute when adding the I18nModule to your application. Thereby, true describes the following behaviour:

Say, you request the translation mail.registration.subject in a de language, and this specific key is missing. This will create a de/mail.missing file in your i18n folder and add the following content:

{
  "registration": {
    "subject": ""
  }
}

CLI

To easily check if your i18n folder is correctly structured you can use the following command: nest-i18n check <i18n-path>

example: nest-i18n check src/i18n

This is very useful inside a CI environment to prevent releases with missing translations.

Breaking changes:

• from V4.0.0 on we changed the signature of the translate method, the language is now optional, if no language is given it'll fallback to the fallbackLanguage

• from V3.0.0 on we load translations based on their directory name instead of file name. Change your translations files to the structure above: info