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Translation library for Angular and Ionic applications.


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Lightweight (±3KB) translation library for Angular applications.

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npm install @ngstack/translate

Using with the application

Create en.json file in the src/app/assets/i18n folder of your application.

  "TITLE": "Hello from NgStack/translate!"

Import TranslateModule into you main application module, configure TranslateService to load during application startup.

You will also need HttpClientModule module dependency.

import { NgModule, APP_INITIALIZER } from '@angular/core';
import { HttpClientModule } from '@angular/common/http';
import { TranslateModule } from '@ngstack/translate';

// needed to load translation before application starts
export function setupTranslateService(service: TranslateService) {
  return () => service.load();

  imports: [
      // options
  providers: [
    // needed to load translation before application starts
      provide: APP_INITIALIZER,
      useFactory: setupTranslateService,
      deps: [TranslateService],
      multi: true
  declarations: [AppComponent],
  bootstrap: [AppComponent]
export class AppModule {}

In the main application template, use the following snippet:

  {{ 'TITLE' | translate }}


Translate Pipe

  • <element>{{ 'KEY' | translate }}</element>
  • <element [attribute]="property | translate"></element>
  • <element attribute="{{ property | translate }}"></element>
  • <element [innerHTML]="'KEY' | translate"></element>
  • <element>{{ 'PROPERTY.PATH' | translate }}</element>
  • <element>{{ 'FORMAT' | translate:params }}</element>
  • (2.3.0) <element [translate]="'KEY'"></element>
  • (2.3.0) <element [translate]="'FORMAT'" [translateParams]="{ msg: hello }"></element>
  • (2.3.0) <element translate="KEY"></element>

Title Service

  • Sets page title value with automatic translation
  • Watches for language changes and updates the title accordingly

Translating application title

Update the localization files for your application and add APP.TITLE resource key:

  "APP": {
    "TITLE": "My Application"

Update the title from the code, the main application component is a perfect place for that:

import { TitleService } from '@ngstack/translate';

export class AppComponent implements OnInit {
  constructor(private titleService: TitleService) {}

  ngOnInit() {

Now every time the language is changed, the page title is going to get changed automatically.

Translate Service

  • Load translations on language change
  • Translation from code
  • Defining translation data from code
  • Merging multiple translations
  • Loading translations from multiple locations
  • Automatic fallback for missing translations
  • Defining supported languages
  • Configurable cache busting
  • Lazy loading support
  • Visual debugging mode to simplify development and testing

Using from code

You can import and use translate service in the code:

export class MyComponent {

  text: string;

  constructor(translate: TranslateService) {

    this.text = translate.get('SOME.PROPERTY.PATH');



Custom language without external files

An example for providing translation data from within the application, without loading external files.

export class AppModule {
  constructor(translate: TranslateService) {
    translate.use('en', {
      'TITLE': 'Hello from @ngstack/translate!'

Formatted translations

You can use runtime string substitution when translating text

    "HELLO_MESSAGE": "Hello, {username}!"

Then in the HTML:

<div>{{ 'FORMATTED.HELLO_MESSAGE' | translate:{ 'username': 'world' } }}</div>

Or in the Code:

export class MyComponent {

  text: string;

  constructor(translate: TranslateService) {

    this.text = translate.get(
      { username: 'world' }



Should produce the following result at runtime:

Hello, world!

You can use multiple values in the format string. Note, however, that TranslateService checks only the top-level properties of the parameter object.

Advanced topics

You can provide custom parameters for the forRoot method of the TranslateModule

interface TranslateSettings {
  debugMode?: boolean;
  disableCache?: boolean;
  supportedLangs?: string[];
  translationRoot?: string;
  translatePaths?: string[];
  activeLang?: string;

For example:

  debugMode: true,
  activeLang: 'fr'

Testing components

When testing localisation with a single translation file it is sometimes hard to tell if a component text switches to a different language. You can simplify testing of the end-applications and components by enabling the debug mode.

While in the debug mode, the service automatically prepends active language id to very translated result. That allows to verify that your components support i18n correctly and do not contain hard-coded text.

  debugMode: true

Now, if using en as the active language, all strings should start with the [en] prefix.

Watching for language change

You can watch for language change event utilising the activeLangChanged event:

export class MyComponent {

  constructor(translate: TranslateService) {

      (event: { previousValue: string; currentValue: string }) => {


Custom translation path

By default TranslateService loads files stored at assets/i18n folder. You can change the TranslateService.translationRoot property to point to a custom location if needed.

  translationRoot: '/some/path'

Loading from multiple locations

To provide multiple locations use the TranslateService.translatePaths collection property.

  translatePaths: ['assets/lib1/i18n', 'assets/lib2/i18n']

The files are getting fetched and merged in the order of declarations, and applied on the top of the default data loaded from TranslateService.translationRoot path.

Cache busting

You can disable browser caching and force application always load translation files by using TranslateService.disableCache property.

  disableCache: true

Define active language

The service takes browser language as an active language at startup. You can use activeLang property to define a custom value and override browser settings.

  activeLang: 'fr'

Restricting supported languages

It is possible to restrict supported languages to a certain set of values. You can avoid unnecessary HTTP calls by providing TranslateService.supportedLangs values.

  supportedLangs: ['fr', 'de']

The service will try to load resource files only for given set of languages, and will use fallback language for all unspecified values.

By default this property is empty and service will probe all language files. The service always takes into account the Active and Fallback languages, even if you do not specify them in the list.

Using with your own pipes

It is possible to use TranslateService with your own implementations.

You can see the basic pipe implementation below:

import { Pipe, PipeTransform } from '@angular/core';
import { TranslateService, TranslateParams } from '@ngstack/translate';

  name: 'myTranslate',
  pure: false
export class CustomTranslatePipe implements PipeTransform {
  constructor(private translate: TranslateService) {}

  transform(key: string, params?: TranslateParams): string {
    return this.translate.get(key, params);

Then in the HTML templates you can use your pipe like following:

  Custom Pipe: {{ 'TITLE' | myTranslate }}

Lazy Loading

To enable Lazy Loading use TranslateModule.forRoot() in the main application, and TranslateModule.forChild() in all lazy-loaded feature modules.

For more details please refer to Lazy Loading Feature Modules

See also

List of alternative libraries you can check out: