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 for the 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 an @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: (config: 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: [
        new QueryResolver(['lang', 'locale', 'l']),
        new HeaderResolver(),
        new CookieResolver(['lang', 'locale', 'l'])
      ],
    }),
  ],
  controllers: [HelloController],
})
export class AppModule {}

Currently, there are two build-in resolvers

Resolver	Default value
QueryResolver	none
HeaderResolver	accept-language
CookieResolver	lang

To implement your own resolver (or custom logic) use the I18nResolver interface.

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

Use with caution! The I18nRequestScopeService uses 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. 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