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

Table of contents

• Versions
• Quick Start
  • Structure
  • Translation File
  • nest-cli.json copy i18n
  • Translation Module
    • Using forRootAsync()
  • Live reloading / Refreshing translations
  • GraphQL usage
  • Parser
    • Live translations / languages
  • Language Resolvers
    • Custom resolver
    • Using forRootAsync()
    • Using Fallbacks
  • Translating with i18n module
    • I18nLang decorator and I18nService
    • I18n decorator
    • I18nRequestScopeService within a custom service using request scoped translation service
  • Pluralize translations
  • Nested translations
  • Translating HttpExceptions

• Breaking changes:

Versions

To keep your setup working use the correct version of nestjs-i18n.

nestjs-i18n version	nestjs version
v7.0.0 or greather	v7.0.0
v6.0.0 or below	v6.0.0

Quick Start

Build in we have a JSON parser (I18nJsonParser) this parser handles to following structure

Structure

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

package.json
package-lock.json
...
src
└── 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"]
}

All the translations are prefixed with the file name (to prevent collisions). Let's say the filename of the translation file is: user.json. To use the HELLO_MESSAGE translation you would use the following key: user.HELLO_MESSAGE.

String formatting is done by: string-format

nest-cli.json copy i18n

If you've created your project using the @nestjs/cli you can edit the nest-cli.json to automatically copy your i18n folder to your output (dist) folder.

{
  "collection": "@nestjs/schematics",
  "sourceRoot": "src",
  "compilerOptions": {
    "assets": ["i18n/**/*"]
  }
}

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, I18nJsonParser } from 'nestjs-i18n';

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

Using forRootAsync()

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

@Module({
  imports: [
    I18nModule.forRootAsync({
      useFactory: (configService: ConfigurationService) => ({
        fallbackLanguage: configService.fallbackLanguage, // e.g., 'en'
        parserOptions: {
          path: path.join(__dirname, '/i18n/'),
        },
      }),
      parser: I18nJsonParser,
      inject: [ConfigurationService],
    }),
  ],
  controllers: [],
})
export class AppModule {}

Live reloading / Refreshing translations

To use live reloading use the watch option in the I18nJsonParser. The I18nJsonParser watches the i18n folder for changes and when needed updates the translations or languages.

I18nModule.forRoot({
  fallbackLanguage: 'en',
  parser: I18nJsonParser,
  parserOptions: {
    path: path.join(__dirname, '/i18n/'),
    // add this to enable live translations
    watch: true,
  },
});

To refresh your translations and languages manually:

await this.i18nService.refresh();

GraphQL usage

When using GraphQL it is required to provide the right context. You can do this by importing the GraphQLModule like this:

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

@Module({
  imports: [
    I18nModule.forRoot({
      fallbackLanguage: 'en',
      parser: I18nJsonParser,
      parserOptions: {
        path: path.join(__dirname, '/i18n/'),
      },
    }),
    GraphQLModule.forRoot({
      // USE THIS TO PROVIDE THE RIGHT CONTEXT FOR I18N
      context: ({ req, connection }) => connection ? { req: connection.context } : { req },
      ...
    }),
  ],
  controllers: [],
})
export class AppModule {}

Parser

A default JSON parser (I18nJsonParser) is included.

To implement your own I18nParser take a look at this example i18n.json.parser.ts.

Live translations / languages

To provide live translations you can return an observable within the extended I18nParser class. For and implementation example you can take a look at the i18n.json.parser.ts.

export class I18nMysqlParser extends I18nParser {
  constructor(
    @Inject(I18N_PARSER_OPTIONS)
    private options: I18nJsonParserOptions,
  ) {
    super();
  }

  async languages(): Promise<string[] | Observable<string[]>> {
    // for example do a database call here
    return observableOf(['nl', 'en']);
  }

  async parse(): Promise<I18nTranslation | Observable<I18nTranslation>> {
    // for example do a database call here
    return observableOf({
      nl: {
        HELLO: 'Hallo',
      },
      en: {
        HELLO: 'Hello',
      },
    });
  }
}

Language Resolvers

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

(note: When using forRootAsync you don't return the resolvers with the rest of the config. You'll need to provide the resolvers like this: example)

@Module({
  imports: [
    I18nModule.forRoot({
      fallbackLanguage: 'en',
      parser: I18nJsonParser,
      parserOptions: {
        path: path.join(__dirname, '/i18n/'),
      },
      resolvers: [
        { use: QueryResolver, options: ['lang', 'locale', 'l'] },
        new HeaderResolver(['x-custom-lang']),
        AcceptLanguageResolver,
        new CookieResolver(['lang', 'locale', 'l']),
      ],
    }),
  ],
  controllers: [HelloController],
})
export class AppModule {}

Currently, there are four built-in resolvers

Resolver	Default value
QueryResolver	none
HeaderResolver	none
AcceptLanguageResolver	N/A
CookieResolver	lang

Custom resolver

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(context: ExecutionContext) {
    let req: any;

    switch (context.getType() as string) {
      case 'http':
        req = context.switchToHttp().getRequest();
        break;
      case 'graphql':
        [, , { req }] = context.getArgs();
        break;
    }

    let lang: string;

    if (req) {
      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({
  fallbackLanguage: 'en',
  parser: I18nJsonParser,
  parserOptions: {
    path: path.join(__dirname, '/i18n/'),
  },
  resolvers: [{ use: QueryResolver, options: ['lang', 'locale', 'l'] }],
});

Using forRootAsync()

I18nModule.forRootAsync({
  useFactory: () => {
    return {
      fallbackLanguage: 'en',
      parserOptions: {
        path: path.join(__dirname, '/i18n'),
      },
    };
  },
  parser: I18nJsonParser,
  resolvers: [{ use: QueryResolver, options: ['lang', 'locale', 'l'] }],
});

Using Fallbacks

To configure multiple fallbacks use fallbacks option. You could handle a single language or multiple ones.

(note: In this example, the translations en fr and pt-BR are needed to work correctly.)

I18nModule.forRoot({
  fallbackLanguage: 'en',
  fallbacks: {
    'en-CA': 'fr',
    'en-*': 'en',
    'fr-*': 'fr',
    pt: 'pt-BR',
  },
  parser: I18nJsonParser,
  parserOptions: {
    path: path.join(__dirname, '/i18n/'),
  },
});

Translating with i18n module

I18nLang decorator and I18nService

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

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

I18n decorator

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

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

Pluralize translations

You can use plurals inside your translations as followed. You need to provide a one, other and zero translation for the pluralization to work.

{
  "day_interval": {
      "one": "Every day",
      "other": "Every {count} days",
      "zero": "Never"
  },
  "cat": {
      "one": "cat",
      "other": "cats",
      "zero": "cats"
  }
}

For i18n to pick the right plural you need to provide a count argument within the translation function.

await i18n.translate('test.day_interval', {
  args: { count: 1 },
});

Nested translations

You can also use nested translation by making use of the translate function inside your translation by doing: $t(KEY). To pass down arguments: $t(KEY, {{\"count\": {count} }}).

{
  "day_interval": {
    "one": "Every day",
    "other": "Every {count} days",
    "zero": "Never"
  },
  "shopping": "We go shopping: $t(test.day_interval, {{\"count\": {count} }})"
}

Translating HttpExceptions

To translate httpexceptions, we need to create a filter and translate the exception message.

import { I18nService } from 'nestjs-i18n';
import {
	ExceptionFilter,
	Catch,
	ArgumentsHost,
	HttpException,
} from '@nestjs/common';
import { Request, Response } from 'express';

@Catch(HttpException)
export class AllExceptionsFilter implements ExceptionFilter {
	constructor(private readonly i18n: I18nService) {}

	async catch(exception: HttpException, host: ArgumentsHost) {
		const ctx = host.switchToHttp();
		const response = ctx.getResponse<Response>();
		const statusCode = exception.getStatus();

		let message = exception.getResponse() as {
			key: string;
			args: Record<string, any>;
		};

		message = await this.i18n.translate(message.key, {
			lang: ctx.getRequest().i18nLang,
			args: message.args,
		});

		response.status(statusCode).json({ statusCode, message });
	}
}

Now we need to use this filter as global filter. Since we are using dependency injection, you cannot have dependency injection if you register your filter with useGlobalFilters(). From the docs, register the filter as global filter as :

import { Module } from '@nestjs/common';
import { APP_FILTER } from '@nestjs/core';

@Module({
  providers: [
    {
      provide: APP_FILTER,
      useClass: AllExceptionsFilter,
    },
  ],
})
export class AppModule {}

Now to use the filter , simply throw exceptions like:

  throw new HttpException(
    { key: 'operations.HELLO', args: { username: 'rubin' } },
	HttpStatus.FORBIDDEN,
     );
    

Breaking changes:

• from V8.0.0 on we changed the internal 18n-middleware for an interceptor this way we can provide the ExecutionContext so that nestjs-i18n works on diffrent protocols was well for example (grpc or websockets). This contains one breaking change. It only applies to your code if you've made a custom resolver. To resolve this breaking change take look at this example. Instead of providing the req in the resolve method, change this to take the ExecutionContext as argument.

• from V6.0.0 on we implemented the I18nParser, by using this we can easily support different formats other than JSON. To migrate to this change look at the Quick start above. There are some changes in the declaration of the I18nModule. Note: the translate function returns a Promise. So you need to call it using await i18n.translate('HELLO');

• 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