ngx-translate Documentation

This is a slightly enhanced version of the original documentation included in ngx-translate's github repo, written by Oliver Combe. Enhancements: Nicer formatting, table of contents on the right side, links in the API, some comments and remarks that might be useful...
Installation
First you need to install the npm module:
npm install @ngx-translate/core --save
Choose the version corresponding to your Angular version:
Angular | @ngx-translate/core | @ngx-translate/http-loader | Tutorial |
---|---|---|---|
13 (ivy only) | 14.x+ | 7.x+ | Tutorial |
10/11/12/13 | 13.x+ | 6.x+ | Tutorial |
9 | 12.x+ | 5.x+ | Tutorial |
8 | 12.x+ | 4.x+ | Tutorial |
7 | 11.x+ | 4.x+ | Tutorial |
6 | 10.x | 3.x | Tutorial |
5 | 8.x to 9.x | 1.x to 2.x | — |
4.3 | 7.x or less | 1.x to 2.x | — |
2 to 4.2.x | 7.x or less | 0.x | — |
Usage
Importing the TranslateModule
Finally, you can use ngx-translate in your Angular project.
You have to import TranslateModule.forRoot()
in the root NgModule of your application.
The forRoot
static method is a convention that provides and configures services at the same time.
Make sure you only call this method in the root module of your application, most of the time called AppModule
.
This method allows you to configure the TranslateModule
by specifying a loader, a parser and/or a missing translations handler.
You can also set the default language.
import {BrowserModule} from '@angular/platform-browser';
import {NgModule} from '@angular/core';
import {TranslateModule} from '@ngx-translate/core';
@NgModule({
imports: [
BrowserModule,
TranslateModule.forRoot({
defaultLanguage: 'en'
})
],
bootstrap: [AppComponent]
})
export class AppModule { }
Usage with SharedModules
If you use a SharedModule
that you import in multiple other feature modules,
you can export the TranslateModule
to make sure you don't have to import it in every module.
@NgModule({
exports: [
CommonModule,
TranslateModule
]
})
export class SharedModule { }
Note: Never call a forRoot
static method in the SharedModule
. You might end up with different instances of the service in your injector tree. But you can use forChild
if necessary.
Lazy loaded modules
When you lazy load a module, you should use the forChild
static method to import the TranslateModule
.
Since lazy loaded modules use a different injector from the rest of your application, you can configure them separately with a different loader/compiler/parser/missing translations handler.
To make a child module extend translations from parent modules use extend: true
. This will cause the service to also
use translations from its parent module.
You can also isolate the service by using isolate: true
. In which case the service is a completely isolated instance (for translations, current lang, events, ...).
Otherwise, by default, it will share its data with other instances of the service (but you can still use a different loader/compiler/parser/handler even if you don't isolate the service).
@NgModule({
imports: [
TranslateModule.forChild({
loader: {provide: TranslateLoader, useClass: CustomLoader},
compiler: {provide: TranslateCompiler, useClass: CustomCompiler},
parser: {provide: TranslateParser, useClass: CustomParser},
missingTranslationHandler: {provide: MissingTranslationHandler, useClass: CustomHandler},
isolate: true
})
]
})
export class LazyLoadedModule { }
Loading language files dynamically
By default, there is no loader available. You can add translations manually using setTranslation
but it is better to use a loader.
You can write your own loader, or import an existing one.
Ngx-translate comes with TranslateHttpLoader
which loads translation files using HttpClient
.
To use it, you need to install the http-loader package from @ngx-translate:
npm install @ngx-translate/http-loader --save
Once you've decided which loader to use, you have to set up the TranslateModule
to use it.
Here is how you would use the TranslateHttpLoader
to load
translations from "/assets/i18n/[lang].json"
. [lang]
is the lang that you're using, for english it could be en
.
You have to create the translate loader inside a factory method if you want to use AoT compilation or Ionic.
export function createTranslateLoader(http: HttpClient) {
return new TranslateHttpLoader(http, './assets/i18n/', '.json');
}
@NgModule({
imports: [
BrowserModule,
HttpClientModule,
TranslateModule.forRoot({
loader: {
provide: TranslateLoader,
useFactory: (createTranslateLoader),
deps: [HttpClient]
}
})
],
bootstrap: [AppComponent]
})
export class AppModule { }
Initialize the TranslateService
for your application
import {Component} from '@angular/core';
import {TranslateService} from '@ngx-translate/core';
@Component({
selector: 'app',
template: `
<div>{{ 'app.hello' | translate:param }}</div>
`
})
export class AppComponent {
param = {value: 'world'};
constructor(translate: TranslateService) {
translate.setDefaultLang('en');
translate.use('en');
}
}
setDefaultLang()
sets the default language. The default language is used
as a fall-back if no translation is found in the currently selected language.
use()
sets the current language for the application. If the selected language is not yet
loaded, the loader is invoked to retrieve the file.
Define the translations
Once you've imported the TranslateModule
, you can put your translations
in a json file that will be imported with the TranslateHttpLoader
.
The following translations should be stored in en.json
.
{
"app.hello": "hello {{value}}"
}
You can also define your translations manually with setTranslation()
.
translate.setTranslation('en', {
"app.hello": 'hello {{value}}'
});
You can also use nested JSON objects — this allows you to create more structured translation files and provide some more context for the translators.
{
"app": {
"hello": "hello {{value}}"
}
}
You can then access the value by using the dot notation, in this case app.hello
.
Work with translations in your components
You can either use the TranslateService
, the TranslatePipe
or the TranslateDirective
to get your translation values.
Using translations in a component
With the service, it looks like this:
translate.get('app.hello', {value: 'world'}).subscribe((res: string) => {
console.log(res);
//=> 'hello world'
});
You might ask yourself, why get() is using a subscription to receive the translation. This is because your language file might not be loaded when the get() function is called. The update is triggered when the loading is complete.
You can also use stream() which is similar to get but also fires when the language is changed.
There is also instant() — a synchronous method that returns the translation value
immediately. This only works if the translation file is already loaded — or the translations
are set using setTranslation()
.
Using translations in templates (TranslatePipe, TranslateDirective)
This is how you do it with the pipe:
<div>{{ 'app.hello' | translate:param }}</div>
And in your component define param
like this:
param = {value: 'world'};
You can construct the translation keys dynamically by using simple string concatenation inside the template:
<ul *ngFor="let language of languages">
<li>{{ 'languages.' + language | translate }}</li>
</ul>
Where languages
is an array member of your component:
languages = ['en', 'fr', 'de'];
You language file would look like this;
{
'languages': {
'en': 'English',
'fr': 'French',
'de': 'German'
}
}
You can also use the output of the built-in pipes uppercase
and lowercase
in order to guarantee
that your dynamically generated translation keys are either all uppercase or all lowercase. For example:
<p>{{ 'roles.' + role | lowercase | translate }}</p>
role = 'ADMIN';
will match the following translation:
{
"roles": {
"admin": "Administrator"
}
}
A plugin called ngx-translate-extract can help you keeping your source code and translation files in sync: It extracts the translation IDs from your source code. This does of course not work with dynamically created IDs like the one above.
This is how you use the directive:
<div [translate]="'HELLO'" [translateParams]="{value: 'world'}"></div>
Or even simpler using the content of your element as a key:
<div translate [translateParams]="{value: 'world'}">HELLO</div>
I recommend not use the pipe instead of the directive because both variants of the directive have issues. The one without a value causes warnings in some IDEs, the first one does currently not properly work with the message compiler plugin.
Using HTML tags in your translations
You can easily use raw HTML tags within your translations.
{
"HELLO": "Welcome to my Angular application!<br><strong>This is an amazing app which uses the latest technologies!</strong>"
}
To render them, simply use the innerHTML
attribute with the pipe on any element.
<div [innerHTML]="'HELLO' | translate"></div>
[innerHTML]
should be safe to use because it uses Angular's DomSanitizer
to filter potentially harmful tags like
<script>
or <style>
.
TranslateService API
Properties
currentLang
: The lang currently useddefaultLang
: The default (fall-back) languagecurrentLoader
: An instance of the loader currently used (static loader by default)
onLangChange (Event Emitter)
An EventEmitter to listen to lang change events. A LangChangeEvent
is an object
with the properties:
Name | Type | Description |
---|---|---|
lang | string | the code of the activated language |
translations | any | an object containing your translations |
Example:
onLangChange.subscribe((event: LangChangeEvent) => {
// do something
);
onTranslationChange (Event Emitter)
An EventEmitter to listen to translation change events.
A TranslationChangeEvent
is an object with the properties:
Name | Type | Description |
---|---|---|
lang | string | the code of the activated language |
translations | any | an object containing your translations |
Example:
onTranslationChange.subscribe((event: TranslationChangeEvent) => {
// do something
);
onDefaultLangChange (Event Emitter)
An EventEmitter to listen to default lang change events.
A DefaultLangChangeEvent
is an object with the following properties:
Name | Type | Description |
---|---|---|
lang | string | the code of the activated language |
translations | any | an object containing your translations |
Example:
onDefaultLangChange.subscribe((event: DefaultLangChangeEvent) => {
// do something
);
setDefaultLang
setDefaultLang(lang: string)
Sets the default language to use as a fallback. A translation is used from the default language, if no translation is found in the current language.
Calling setDefaultLang
uses the loader to retrieve the language and
updates the list of available languages which can be retrieved using getLangs
.
getDefaultLang
getDefaultLang(): string
Returns the default language.
use
use(lang: string): Observable<any>
Changes the currently active language. This invokes the current loader to retrieve the translations if the language is not yet loaded.
Calling use
uses the loader to retrieve the language and
updates the list of available languages which can be retrieved using getLangs
.
getTranslation
getTranslation(lang: string): Observable<any>
Gets an object of translations for a given language with the current loader.
setTranslation
setTranslation(lang: string, translations: Object, shouldMerge: boolean = false)
Manually sets an object of translations for a given language,
set shouldMerge
to true if you want to append the translations instead of replacing them.
Using setTranslation
updates the list of available languages which can be retrieved using getLangs
.
addLangs
addLangs(langs: Array<string>)
Add new languages to the list. This does not invoke the loader to retrieve the languages.
getLangs
getLangs(): string
Returns an array of currently available languages. The list can be extended
calling setDefaultLang
, use
, setTranslation
oraddLangs
.
get
get(key: string|Array<string>, interpolateParams?: Object): Observable<string|Object>
Gets the translated value of a key (or an array of keys) or the key if the value was not found.
The Observable
fires after the language file is loaded. Use stream
if you
want to get updates to language changes, too.
getStreamOnTranslationChange
getStreamOnTranslationChange(key: string|Array<string>, interpolateParams?: Object): Observable<string|Object>
Returns a stream of translated values of a key (or an array of keys) or the key if
the value was not found. Without any onTranslationChange
`` events this returns the same
value as get
but it will also emit new values whenever the translation changes.
stream
stream(key: string|Array<string>, interpolateParams?: Object): Observable<string|Object>
Returns a stream of translated values of a key (or an array of keys) or the key if
the value was not found. Without any onLangChange
events this returns the same
value as get
but it will also emit new values whenever the used language changes.
instant
instant(key: string|Array<string>, interpolateParams?: Object): string|Object
Gets the instant translated value of a key (or an array of keys).
This method is synchronous and the default file loader is asynchronous. You are responsible for knowing when your translations
have been loaded and it is safe to use this method. If you are not sure then you should use the get
method instead.
set
set(key: string, value: string, lang?: string)
Sets the translated value of a key.
reloadLang
reloadLang(lang: string): Observable<string|Object>
Calls resetLang
and retrieves the translations object for the current loader
resetLang
resetLang(lang: string)
Removes the current translations for this lang.
You will have to call use
, reloadLang
or getTranslation
again
to be able to get translations
getBrowserLang
getBrowserLang(): string | undefined
Returns the current browser lang if available, or undefined otherwise.
getBrowserCultureLang
getBrowserCultureLang(): string | undefined
Returns the current browser culture language name (e.g. "de-DE" if available), or undefined otherwise
TranslateParser API
The TranslateParser
service has 2 methods which might sometimes be useful:
interpolate
interpolate(expr: string | Function, params?: any): string
Interpolates a string to replace parameters or calls the interpolation function with the parameters.
Example:
parser.interpolate('This is a {{key}}!', {key: 'banana'})
Returns This is a banana!
Example:
parser.interpolate((params) => `This is a ${params.key}`, {key: 'banana'})
Returns This is a banana!
getValue
getValue(target: any, key: string): any
Gets a value from an object by composed key. The .
is interpreted as sub-object:
Example:
parser.getValue({ key1: { keyA: 'value' }}, 'key1.keyA')
Returns value
.
Write & use your own loader
If you want to write your own loader, you need to create a class that
implements TranslateLoader
. The only required method is getTranslation
that must return an Observable
. If your loader is synchronous, just use Observable.of
to create an observable from your static value.
Example
class CustomLoader implements TranslateLoader {
getTranslation(lang: string): Observable<any> {
return Observable.of({KEY: 'value'});
}
}
Once you've defined your loader, you can provide it in your configuration by adding it to its providers
property.
@NgModule({
imports: [
BrowserModule,
TranslateModule.forRoot({
loader: {provide: TranslateLoader, useClass: CustomLoader}
})
],
bootstrap: [AppComponent]
})
export class AppModule { }
How to use a compiler to preprocess translation values
By default, translation values are added "as-is". You can configure a compiler
that implements TranslateCompiler
to pre-process translation values when they are added (either manually or by a loader). A compiler has the following methods:
compile(value: string, lang: string): string | Function
: Compiles a string to a function or another string.compileTranslations(translations: any, lang: string): any
: Compiles a (possibly nested) object of translation values to a structurally identical object of compiled translation values.
Using a compiler opens the door for powerful pre-processing of translation values. As long as the compiler outputs a compatible interpolation string or an interpolation function, arbitrary input syntax can be supported.
How to handle missing translations
You can setup a provider for the MissingTranslationHandler
in the bootstrap of your application (recommended), or in the providers
property of a component. It will be called when the requested translation is not available. The only required method is handle
where you can do whatever you want. If this method returns a value or an observable (that should return a string), then this will be used. Just don't forget that it will be called synchronously from the instant
method.
You can use useDefaultLang
to decide whether default language string should be used when there is a missing translation in current language. Default value is true. If you set it to false, MissingTranslationHandler
will be used instead of the default language string.
Example:
Create a Missing Translation Handler
import {MissingTranslationHandler, MissingTranslationHandlerParams} from '@ngx-translate/core';
export class MyMissingTranslationHandler implements MissingTranslationHandler {
handle(params: MissingTranslationHandlerParams) {
return 'some value';
}
}
Setup the Missing Translation Handler in your module import by adding it to the forRoot
(or forChild
) configuration.
@NgModule({
imports: [
BrowserModule,
TranslateModule.forRoot({
missingTranslationHandler: {provide: MissingTranslationHandler, useClass: MyMissingTranslationHandler},
useDefaultLang: false
})
],
providers: [
],
bootstrap: [AppComponent]
})
export class AppModule { }
FAQ
I want to hot reload the translations in my application but reloadLang
does not work
If you want to reload the translations and see the update on all your components
without reloading the page, you have to load the translations manually and
call setTranslation
function which triggers onTranslationChange
.
Plugins
- Localize Router by @meeroslav: An implementation of routes localization for Angular. If you need localized urls (for example /fr/page and /en/page).
- browser.i18n Loader by @pearnaly: loader for native translation files of browser extensions.
- ngx-translate-extract by @biesbjerg: Extract translatable strings from your projects
- MessageFormat Compiler by @lephyrus: Compiler for ngx-translate that uses messageformat.js to compile translations using ICU syntax for handling pluralization, gender, and more
- ngx-translate-multi-http-loader by @denniske: Fetch multiple translation files with ngx-translate.
- ngx-translate-cache by @jgpacheco: Simplified version of localize-router. If you are already using localize-router you don't need this extension. This extension is aimed only to facilitate language caching.
- ngx-translate-module-loader by @larscom: Fetch multiple translation files (http) with ngx-translate. Each translation file gets it's own namespace out of the box and the configuration is very flexible.
- ngx-translate-lint by @svoboda-rabstvo: Simple CLI tools for check ngx-translate keys in whole app
- ngx-translate-cut by @bartholomej: Simple and useful pipe for cutting translations ✂️
Editors
- BabelEdit — translation editor for JSON files