NestJS Translator Module

A simple and lightweight module and exception filter to translate and organize your NestJS app messages (strings).

Installation

1 - Use the npm package manager to install this module :

npm i nestjs-translator

2 - Import the nestjs-translator module in the module that you want to use, like this :

app.module.ts

import { Module } from '@nestjs/common';
import { TranslatorModule } from 'nestjs-translator';

@Module({
  imports: [
    TranslatorModule.forRoot({
      global: true,
      defaultLang: 'en',
      translationSource : process.cwd() + '/src/i18n'
    }),
  ],
  controllers: [AppController],
  providers: [AppService],
})
export class AppModule {}

NOTICE ::: If you define global option to true then your NestJS app can access the translator module in other modules.

I recommend you to use global : true.

3 - Create your translation source :

You can create translation sources/strings particularly.

The default path for translation sources is /src/i18n.

So we create some translation sources (with JSON format) in our project like this :

    Your project
    ├── dist
    ├── src
        └── i18n
            └── en
                ├── common.json
                └── cats.json
            └── fa
                ├── common.json
                └── cats.json

In this example en is a translation source folder for english language and fa is translation source folder for farsi (persian) language.

Let's add some content into our files.

/src/i18n/en/common.json

{
    "you_are_not_logged_in" : "You are not logged in, please login now!",
    "welcome" : "Welcome to new NestJS app"
}

/src/i18n/fa/common.json

{
    "you_are_not_logged_in" : "شما وارد سیستم نشده اید",
    "welcome" : "خوش آمدید"
}

Use it !

There's no more configuration step, you can use the translator as a service in the controller.

import { Controller, Get } from '@nestjs/common';
import { TranslatorService } from 'nestjs-translator';

@Controller()
export class AppController {
  constructor(
    private translator: TranslatorService,
  ) {}

  @Get()
  getHello(): string {
    return this.translator.translate('welcome', {
      lang: 'fa',
    });
  }
}

Start your NestJS app :

npm run start:dev

See the result : http://localhost:3000

Replaceable fields

You can replace parts of the text simply by using ${} syntax in the translation source.

/src/i18n/en/common.json

{
    "welcome" : "Welcome to new ${appName} app"
}

Specify replace in the translate method options like this :

import { Controller, Get } from '@nestjs/common';
import { TranslatorService } from 'nestjs-translator';

@Controller()
export class AppController {
  constructor(
    private translator: TranslatorService,
  ) {}

  @Get()
  getHello(): string {
    return this.translator.translate('welcome', {
      lang: 'en',
      replace: {
        appName: 'NestJS',
      },
    });
  }
}

You should see this as the output :

Welcome to new NestJS app.

Translator Filter

TranslatorFilter is a nice feature to automate the http exception translation.

Add it into your controller by using @UseFilters(TranslatorFilter) decorator:

import {
  Controller,
  Get,
  HttpException,
  HttpStatus,
  UseFilters,
} from '@nestjs/common';
import { TranslatorService, TranslatorFilter } from 'nestjs-translator';

@Controller()
@UseFilters(TranslatorFilter)
export class AppController {
  constructor(private translator: TranslatorService) {}

  @Get()
  getHello(): string {
    throw new HttpException('Unauthorized', HttpStatus.UNAUTHORIZED);
  }
}

Define the key.

/src/i18n/en/common.json

{
    "Unauthorized" : "You are not logged in, please login now!"
}

Request key extractor

You can have dynamic language for the http exception filter (TranslatorFilter).

We're assuming that you have an attached user on your ExpressJS Request object.

Then we can use a function called requestKeyExtractor in the module configuration options.

app.module.ts

import { Module } from '@nestjs/common';
import { TranslatorModule } from 'nestjs-translator';

@Module({
  imports: [
    TranslatorModule.forRoot({
      global: true,
      defaultLang: 'en',
      requestKeyExtractor: req => { 
        if(req.user){
            return req.user.language
        }
        return null;
      }, 
    }),
  ],
  controllers: [AppController],
  providers: [AppService],
})
export class AppModule {}

Or maybe using a header to recognise the language :

import { Module } from '@nestjs/common';
import { TranslatorModule } from 'nestjs-translator';

@Module({
  imports: [
    TranslatorModule.forRoot({
      global: true,
      defaultLang: 'en',
      requestKeyExtractor: req => req.get('language'), 
    }),
  ],
  controllers: [AppController],
  providers: [AppService],
})
export class AppModule {}