How to translate your Angular app with ngx-translate

How to translate your Angular app with ngx-translate

Who is this tutorial for?

This tutorial is for Angular developers who want to translate their application into multiple languages. It covers Angular 8 - 15 together with the corresponding ngx-translate versions.

If you are, for some reason, still using an older Angular version, please take a look at the following tutorials:

If you are not sure which translation method to use with your Angular application, you might take a look at our other tutorials:

How to use ngx-translate with Angular

This tutorial guides you through the following steps

Optional: Create an Angular project

For this tutorial you'll start with a simple demo application. I assume that you already have basic knowledge of Angular, and AngularCLI is already installed on your system. You can, of course, skip this step and use your existing project.

Create an empty new project:

ng new translation-demo

The ng client now asks you if you want to add a router and which CSS style / to use. It does not matter which one you choose.

? Would you like to add Angular routing? No
? Which stylesheet format would you like to use? CSS

Finally, start the new project:

cd translation-demo
ng serve

Open your browser and visit the following URL: http://localhost:4200. You should see something similar to this:

Your first Angular application
Default Angular Application at the first start.

Here's the step-by-step guide on how to use NGX-Translate with Angular:

Step 1: Add ngx-translate your Angular application

If you've followed the into step, abort the server with CTRL-C.

Enter the following line in the terminal:

npm install @ngx-translate/core @ngx-translate/http-loader

The @ngx-translate/core contains the core routines for the translation: The TranslateService, the translate pipe and more.

The @ngx-translate/http-loader loads the translation files dynamically from your webserver.

Step 2: Set up the TranslateModule and TranslateService

Start by initializing the TranslateModule in your app.module.ts. The required changes to that file are highlighted in blue:

import { NgModule } from '@angular/core';
import { BrowserModule } from '@angular/platform-browser';

import { AppComponent } from './app.component';

// import ngx-translate and the http loader
import {TranslateLoader, TranslateModule} from '@ngx-translate/core';
import {TranslateHttpLoader} from '@ngx-translate/http-loader';
import {HttpClient, HttpClientModule} from '@angular/common/http';

@NgModule({
    declarations: [
        AppComponent
    ],
    imports: [
        BrowserModule,

        // ngx-translate and the loader module
        HttpClientModule,
        TranslateModule.forRoot({
            loader: {
                provide: TranslateLoader,
                useFactory: HttpLoaderFactory,
                deps: [HttpClient]
            }
        })
    ],
    providers: [],
    bootstrap: [AppComponent]
})
export class AppModule { }

// required for AOT compilation
export function HttpLoaderFactory(http: HttpClient): TranslateHttpLoader {
    return new TranslateHttpLoader(http);
}

The HttpLoaderFactory function is required for AOT (ahead of time) compilation in your project.

Now switch to app.component.ts :

import { Component } from '@angular/core';
import {TranslateService} from "@ngx-translate/core";

@Component({
  selector: 'app-root',
  templateUrl: './app.component.html',
  styleUrls: ['./app.component.css']
})
export class AppComponent {
  constructor(private translate: TranslateService) {
    translate.setDefaultLang('en');
    translate.use('en');
  }
}

Add TranslateService to the constructor parameters to make it available in the component.

Set the default language of your application using translate.setDefaultLang('en'). The default language is the fall-back language, that is used if a translation can not be found.

Set the current language to English by calling translate.use('en'). You'll learn more about switch languages at runtime later in this tutorial.

Let's also clean up app.component.html with this simple text:

<div>
    <h1>Translation demo</h1>
    <p>This is a simple demonstration app for ngx-translate</p>
</div>

Reloading the app seems to work, but a look at the browser console shows the following error:

Failed to load resource: the server responded with a status of 404 (Not Found) http://localhost:4200/assets/i18n/en.json

This is because the HttpLoader tries to load the default language from /assets/i18n/en.json from the server — and we've not yet created that file.

Step 3: Create your JSON translation file

Each language is stored in a separate JSON file. Let's create the JSON file for the English translation: assets/i18n/en.json . Use the texts from the app.components.html . Use a translation ID for each text.

ngx-translate can read 2 JSON formats:

flat json

{
  "demo.title": "Translation demo",
  "demo.text": "This is a simple demonstration app for ngx-translate"
}

or

nested json recommended

{
    "demo": {
        "title": "Translation demo",
        "text": "This is a simple demonstration app for ngx-translate"
    }
}

The translations can, in both cases, be accessed using demo.title and demo.text.

Flat vs nested JSON files

Displaying nested JSON files in BabelEdit as a tree
BabelEdit helps you navigate JSON files, displaying them as a tree.

I prefer the nested (aka namespaced) JSON format because it creates a cleaner structure.

Tools like BabelEdit can display the JSON file as a tree, allowing you to focus on the part of your application you are currently working on.

It's a good practice to create detailed keys — your translators will love the additional context they provide!

E.g. event.confirm-list.title. This gives you a good overview in which context the translations are used. This key is used on the events screen in a list that should confirm events. You also see that event.confirm-list.confirm-button is used in the same context. This not only helps you during development but also helps the translator.

The flat format might include keys which can't be used in the nested format. E.g. the flat version can use demo and demo.title which is not possible with the nested format since demo can't have a text and children at the same time. If you want to convert the flat format into the nested format you'll have to clean up these keys. So: Better use with the nested right from the start.

Don't use translation text as IDs

It is also possible to use the original text as a key for your translation message. I really recommend not doing this!

E.g. in your de.json file it would look like this:

{
    "Translation demo": "Übersetzungsdemo",
    "This is a simple demonstration app for ngx-translate": "Dies ist ein einfaches Beispielprojekt für ngx-translate"
}

The problem is that each change in your main language automatically kills your other translation files. E.g, if you decide to add a "." at the end of "This is a simple demonstration app for ngx-translate." that key is now missing from the de.json and is not displayed. At the same time, the old key "This is a simple demonstration app for ngx-translate" (without the final period) is an unused entry in the file — with a small change that is really hard to spot.

Apart from that, using the translation texts also does not contain any context information. You end up with a list of 100 or more text snippets that provide no information about where they are used.

Step 4: Use translations in your templates and code

Simple text without parameters

Now edit the app.component.html and replace the static texts with references to the messages in the en.json file.

You have 3 choices when it comes to adding translations. All options should lead to the same result — but that's not true in practice:

  • {{'id' | translate}} — translation pipe recommended
    • works in all use-cases
    • acceptable readability
    • also supports other pipes — e.g. making the translation string uppercase,...
  • <element [translate]="'id'"></element> — translation directive, id as attribute value deprecated
    • does (currently) not work with the more complex translation texts — see our section on Pluralization
  • <element translate>id</element> — translation directive, id as a child deprecated
    • shows errors/warnings in some IDEs (e.g. PhpStorm: translate requires a value )
    • quite unreadable syntax when adding parameters

So: If possible go with variant 1.

app.component.html:

<div>
    <h1>{{ 'demo.title' | translate }}</h1>

    <!-- translation: translation pipe -->
    <p>{{ 'demo.text' | translate }}</p>

    <!-- translation: directive (key as attribute)-->
    <p [translate]="'demo.text'"></p>

    <!-- translation: directive (key as content of element) -->
    <p translate>demo.text</p>
</div>

Using parameters in your translations

ngx-translate also supports simple parameters in translations out of the box. They are passed as an object, the keys can be used in the translation strings.

  • {{'id' | translate: {parameter:value} }}
  • <element [translate]="'id'" [translateParams]="{parameter:value}"></element>
  • <element translate [translateParams]="{parameter:value}">id</element>

In your app.component.html, it looks like this.

<!-- translation with parameters: translation pipe -->
<p>{{ 'demo.greeting' | translate:{'name':'Andreas'} }}</p>

<!-- translation: directive (key as attribute) -->
<p [translate]="'demo.greeting'" [translateParams]="{name: 'Andreas'}"></p>

<!-- translation: directive (key as content of element)-->
<p translate [translateParams]="{name: 'Andreas'}">demo.greeting</p>

You can of course pass parameters from your component's .ts file, too.

You also have to extend the en.json with the new demo.greetings id. Translation parameters are put between {{ and }}:

{
  "demo": {
    "title": "Translation demo",
    "text": "This is a simple demonstration app for ngx-translate",
    "greeting": "Hello {{name}}!"
  }
}

Using translations in your components (typescript code)

Sometimes you have to translate messages in your code and not only the template. You can do that with the get() and instant() methods of the TranslateService:

translate.get('demo.greeting', {name: 'John'}).subscribe((res: string) => {
    console.log(res);
});

You might wonder, why get() returns an observable that you have to subscribe to. This is because ngx-translate handles language switches at runtime. The observable fires if the language is switched!

If you are 100% sure that your translations are already loaded (e.g. by using static translations instead of the translation loader) you can also use instant().

console.log(translate.instant('demo.greeting', {name: 'John'}));

Using HTML formatted messages

It's also possible to use HTML formatted messages in your translations.

{
  "demo": {
    "paragraph": "Try <strong>BabelEdit</strong>! This translation editor is made for <strong>ngx-translate</strong>!"
  }
}

To render them, simply use the innerHTML attribute with the pipe on any element.

<div [innerHTML]="'demo.paragraph' | translate"></div>

[innerHTML] should be safe to use because it uses Angular's DomSanitizer to filter potentially harmful tags like <script> or <style>.

More complex translation texts (Pluralization & Selections)

ngx-translate also supports more complex translation parameters including so-called pluralization and selections. E.g. instead of using

  • You have 5 apple(s) in your basket.

It can automatically choose the right form the following:

  • You have no apple in your basket.
  • You have one apple in your basket.
  • You have 5 apples in your basket.

This does not work out-of-the box but can be done with a plugin called ngx-translate-messageformat-compiler. It uses ICU format (ICU stands for International Components for Unicode) and is a wildly used format for specifying complex translation texts. I'll show you how in the Pluralization section later in this tutorial.

Step 5: Translating your JSON files

You are a programmer, and you are right — editing a single JSON file is easy. We all do it all day long: package.json, composer.json — all fine. I sometimes forget to add or remove a comma, but this is not an issue.

But JSON translation files are a completely different story. Why?

Why JSON translation files are a pain to edit

1. You have to keep multiple files in sync

Each change that you make to a translation ID — like adding, removing or renaming — has to be done on all language files. Yes: en.json, it.json, fr.json, de.json,... all need the same treatment.

2. You end up with differences

Sooner or later you'll end up with differences in the language files — no matter how disciplined you are. Just one small edit here... and you forget about updating fr.json and de.json...

3. You try to fix it with a diff / compare tool

Now you try to use some diff tool to find out what the differences are: Which IDs are in which file? What is missing? And guess what: You diff tools shows tons of changes...

Comparing JSON translation files in AraxisMerge
A diff/merge tool is obviously not the best choice for managing translation files.

Above is a diff of 2 JSON files in AraxisMerge — which is a really good diff / merge tool btw... But it's simply the wrong tool for the job...

Install BabelEdit (Free trial, no account required)

Editing your JSON translation files with BabelEdit
BabelEdit shows you the translation strings in all JSON files at the same time.

Things are easy as long as you are only working with a single translation file. But as soon as you add a second language it becomes quite hard work to maintain both files. Not to speak of 5 or more languages.

To get started with BabelEdit download it from here:

BabelEdit is a professional translation editor that works with the common web development frameworks including Angular and ngx-translate. It comes with a lot of nice features that make your daily work much easier:

  • Edit all translations in parallel — stop switching between json files all the time
  • All your edits stay in sync all the time
  • Spell checking for each language
  • Autofill translations from Google Translate
  • Import / Export to and from Excel / CSV / Google Spread Sheets for easy exchange with your translators

Add your Angular Project to BabelEdit

Start by selecting the ngx-translate project template:

Create an Angular translation project with BabelEdit
Create an ngx-translate project in BabelEdit

Now drag & drop your assets/i18n -folder onto the main window.

Using BabelEdit to translate an Angular application using ngx-translate
Drop the folder with your translation files onto BabelEdit

BabelEdit now asks you for the languages contained in the files — making guesses from the file name.

Confirm translation file names and language codes.
Confirm the translation file names and languages

In the same dialog, click on the Add button again to add a new language. Choose New from the menu that opens here:

Confirm translation file names and language codes.
Add new languages to your project

In the new dialog select the language you want to add and click on Ok. BabelEdit automatically chooses the file name based on the language code and puts it into the same directory where the other language file already exists.

Finally, set the primary language to en-US — it's required for the automatic translation feature of BabelEdit:

Set the primary language for your ngx-translate project.
Set the primary language to en-US

After that close the dialog.

Preview your app in other languages using Google Translate or DeepL

This is not a tutorial about BabelEdit but let me show you one awesome features called PreTranslate — it simply takes all your texts and translates them using Google Translate, DeepL or Bing Translate.

Click Pre-Translate in the menu bar, click Ok in the dialog that opens.

Confirm translation file names and language codes.
Use Pre-Translate to automatically translate your JSON files into other languages.

Press Save. BabelEdit asks you to save the project file. Enter angular-demo.babel as file name. This also saves your en.json and de.json files.

Step 6: Switching languages at runtime

Adding a language selector

Let's now update the UI to switch between the language files you've just created:

Reloading the app will not show any differences — this is because you've set the default language to en in app.component.ts .

Make the following changes to the app.component.html to add a simple language switcher:

<button (click)="useLanguage('en')">en</button>
<button (click)="useLanguage('de')">de</button>

Add the following method to the app.component.ts

useLanguage(language: string): void {
    this.translate.use(language);
}

As you might remember, you've used setDefaultLang('en') in the constructor. The default language is the fall-back that is used if a translation is not present in your selected language.

So if you suddenly see English text even if you've selected another language, the reason is usually that your translation files are out-of-sync, and you've not yet translated that string to the other language.

Getting the browser default language

The TranslateService contains 2 methods to receive the language set in the user's browser:

Step 7: Extract translations from source code using ngx-translate-extract

Keeping the JSON files and your app in sync might become a challenge for more complex applications.

The good thing: Kim Biesbjerg created a tool called ngx-translate-extract. It scans your Angular app for the use of translations and adds new translations to your JSON files.

Add ngx-translate-extract to your project

Start by adding it to your project:

npm install @bartholomej/ngx-translate-extract @biesbjerg/ngx-translate-extract-marker
The original version of the extract tool is `@biesbjerg/ngx-translate-extract` but this one does not work with Angular 13 anymore. The author did not update the tool for quite some time. So, if you see the following error while using @biesbjerg/ngx-translate-extract, switching to @bartholomej/ngx-translate-extract should fix the issue.
const text = "node:internal/modules/cjs/loader:979
    throw new ERR_REQUIRE_ESM(filename, true);
    ^

Error [ERR_REQUIRE_ESM]: require() of ES Module .../node_modules/@angular/compiler/fesm2015/compiler.mjs not supported.
Instead change the require of .../node_modules/@angular/compiler/fesm2015/compiler.mjs to a dynamic import() which is available in all CommonJS modules.
at Object.&lt;anonymous&gt; (.../@biesbjerg/ngx-translate-extract/dist/parsers/pipe.parser.js:3:20)
at Object.&lt;anonymous&gt; (.../@biesbjerg/ngx-translate-extract/dist/cli/cli.js:6:23)
at Object.&lt;anonymous&gt; (.../@biesbjerg/ngx-translate-extract/bin/cli.js:3:1) {"{"}
   code: 'ERR_REQUIRE_ESM'

You can add the following lines to your package.json to make using the tool more convenient:

"scripts": {
    "extract-translations": "ngx-translate-extract --input ./src --output ./src/assets/i18n/*.json --clean --sort --format namespaced-json --marker _"
}

Let's take a look at the parameters:

  • --input ./src
    Sets the source directory in which to look for translations. The default is to scan all html and ts files. You can use an additional --patterns parameter to specify other file extensions.
  • --output ./src/assets/i18n/*.json
    This specifies which files to update. The example here updates all existing language files in your ./src/assets/i18n folder that end with json . To add new languages simply add a new (empty) file to the translation folder. You can also list individual files if you prefer being more precise about what to update.
  • --clean
    This option removes all translations that are not found in the source files. Usually it's a good idea to enable this to keep files consistent.
  • --sort
    Sorts the JSON files.
  • --format namespaced-json
    Creates the JSON files with the nested object structure as you used in this tutorial.
  • --marker _
    ngx-translate-extract can search your TypeScript files for strings to translate. You have to surround the strings with a marker function e.g. _('app.title') . See below.

Extracting translations

A simple command now updates your JSON files:

npm run extract-translations

Using translatable strings in your TypeScript files

Sometimes you have to add translatable strings to your TypeScript code. ngx-translate-extract needs a way to distinguish between these strings and all the other strings in your application.

This is where the marker function comes into play. The function itself does nothing — it only passes the string as a result.

import { marker } from '@biesbjerg/ngx-translate-extract-marker';

{
    let messageBoxContent = marker('messagebox.warning.text');
}

Using marker might not be the best choice for a name so feel free to rename it to whatever suits you. I prefer _. The extract module detects the function name you are using based on the import.

import { marker as _ } from '@biesbjerg/ngx-translate-extract-marker';

{
    let messageBoxContent = _('messagebox.warning.text');
}

You can now use the pipe or directive to display the translated string:

<div>{{ messageBoxContent | translate }}</div>

Step 7: Pluralization in Angular in ngx-translate with ICU

Sometimes it's not enough to simply add a value to your translations. There are cases where parts or event the whole sentence has to change.

Think about the following situation: You want to display the number of images a user has uploaded.

  • No image uploaded yet.
  • One image uploaded.
  • 123 images uploaded.

Or you want to display a dynamic value:

  • My favorite color is green.
  • My favorite color is red.
  • My favorite color is blue.

The ngx-translate-messageformat-compiler is what you need now! It parses messages using the ICU syntax.

Install the plugin using the following commands:

npm install ngx-translate-messageformat-compiler @messageformat/core

Next you have to tell ngx-translate to use the message format compiler for rendering the translated messages in app.module.ts :

import {BrowserModule} from '@angular/platform-browser';
import {NgModule} from '@angular/core';
import {AppRoutingModule} from './app-routing.module';
import {AppComponent} from './app.component';

// import ngx-translate and the http loader
import {TranslateCompiler, TranslateLoader, TranslateModule} from '@ngx-translate/core';
import {TranslateHttpLoader} from '@ngx-translate/http-loader';
import {HttpClient, HttpClientModule} from '@angular/common/http';

// import ngx-translate-messageformat-compiler
import {TranslateMessageFormatCompiler} from 'ngx-translate-messageformat-compiler';

@NgModule({
    declarations: [
        AppComponent
    ],
    imports: [
        BrowserModule,
        AppRoutingModule,

        // configure the imports
        HttpClientModule,
        TranslateModule.forRoot({
            loader: {
                provide: TranslateLoader,
                useFactory: HttpLoaderFactory,
                deps: [HttpClient]
            // highlight-start
            },

            // compiler configuration
            compiler: {
                provide: TranslateCompiler,
                useClass: TranslateMessageFormatCompiler
            }
            // highlight-end
        })
    ],
    providers: [],
    bootstrap: [AppComponent]
})

export class AppModule {
}

// required for AOT compilation
export function HttpLoaderFactory(http: HttpClient) {
    return new TranslateHttpLoader(http);
}

Update app.component.html to render the new demo messages:

<div>
  <h2>ngx-translate-messageformat-compiler demo</h2>

  <h3>Pluralization</h3>
  <ul>
    <li translate="" [translateParams]="{ count: 1 }">icu.pluralization</li>
    <li>{{'icu.pluralization' | translate:{ 'count': 2 } }}</li>
  </ul>

  <h3>Selection</h3>
  <ul>
    <li translate [translateParams]="{ 'gender': 'male', 'product': 'BabelEdit' }">icu.select</li>
    <li>{{'icu.select' | translate:{ 'gender': 'other', 'product': 'BabelEdit' } }}</li>
  </ul>

  <button (click)="useLanguage('en')">en</button>
  <button (click)="useLanguage('de')">de</button>
</div>

For some reason not obvious to me, this following syntax does not work with the message compiler. Or better said: It works but gives an error in the browser console.

<p [translate]="'demo.greeting'" [translateParams]="{name: 'Andreas'}"></p>

<li [translate]="'icu.select'" [translateParams]="{ 'gender': 'female', 'product': 'BabelEdit' }"></li>

Finally, update the en.json files with the new ICU syntax:

{
	"demo": {
		"greeting": "Hello {name}!",
		"text": "This is a simple demonstration app for ngx-translate",
		"title": "Translation demo"
	},
	"icu": {
		"pluralization": "There {count, plural, =0{is no apple} one{is one apple} other{there are several apples}}.",
		"select": "{gender, select, male{His uses} female{She uses} other{They use }} {product}"
	},
	"messagebox": {
		"warning": {
			"text": "Warning!"
		}
	}
}

and de.json

{
	"demo": {
        "greeting": "Hallo {name}!",
        "text": "Dies ist eine einfache Applikation um die Funktionen von ngx-transalte zu demonstrieren.",
		"title": "Übersetzungs-Demo"
	},
    "icu": {
		"pluralization": "Da {count, plural, =0{ist kein Apfel} one{ist ein Apfel} other{sind mehrere Äpfel}}.",
		"select": "{gender, select, male{Er verwendet} female{Sie verwendet} other{Sie verwenden }} {product}."
	},
    "messagebox": {
		"warning": {
			"text": "Warnung!"
		}
	}
}

Please note that the ICU templates used by the message parser use single braces {} to enclose parameters — in contrast to the template format of ngx-translate.

This is why you also have to replace the {{name}} in demo.greeting with {name}.

You can read more about the ICU syntax here: ICU User Guide.

How to fix glitches when using TranslateLoader

The translation files are loaded after the application is initialized, this is why you can see the translation message IDs for a short time.

The easiest way to avoid this is to add your main language as static data to your application. You'll still see a small glitch when you start the application with another language — but this time it's your main language that is displayed and not the translation IDs.

If this is also not acceptable you can either bundle your application with all languages or build separate bundles for each language.

First enable loading of JSON files in your tsconfig.app.json

"compilerOptions": {
    ...
    "resolveJsonModule": true,
    "esModuleInterop": true
    ...
},

Open your app.component.ts and load your default language at the top:

import defaultLanguage from "./../assets/i18n/en.json";

Change the constructor to set the translations from the file:

constructor(private translate: TranslateService) {
    translate.setTranslation('en', defaultLanguage);
    translate.setDefaultLang('en');
}

Conclusion

With ngx-translate it's easy to create a multilingual version of your Angular app.

Use ngx-translate-extract to keep your translation files up-to-date.

Finally, BabelEdit helps you to mange and edit your translations.