Angular i18 internationalization, language change programmatically

Question

from this link I tried to implement the i18 internationalization in my Angular 6 app in order to translate in english and italian some text and datetime in my html template.

https://next.angular.io/guide/i18n

I understood that this function consist in 3 phases:

1) Define translation text. No problem, I created a folder src/locale folder with 2 files messages.en.xlf (and message.it.xlf); here is an example for en version.

<trans-unit id="introductionHeader" datatype="html">
  <source>Hello i18n! (en-EN)</source>
  <note priority="1" from="description">An introduction header for this sample</note>
  <note priority="1" from="meaning">User welcome</note>
</trans-unit>

2) link this text to html pages with appropriates tag, and also here no problem, there is my example tag in my app.translations.html.

<h1 i18n="User welcome|An introduction header for this sample">
    Hello i18n!
</h1>

Now, I read the way (3. phase) to localize the app during startup (some editing in Angular.json file and start ng serve with configuration option); but, instead of this, I would change the language of the app programmatically. In other words, I want a command such as

SwitchAppLanguage('en')

for example, so that the user can change it self by a button or the app can do this reading the browser default language. How can I do this?

Thank you very much!

Edit: I tried to edit my angular.json file in this way

"configurations": {
  "production": {
     "i18nFile": "src/locale/messages.it.xlf",
     "i18nFormat": "xlf",
     "i18nLocale": "it",
(...)

And, after ng build and ng serve, I expect to see the italian text but it doesn't happens (and the app start and serve correctly). What do I wrong? Thanks!

Answer 1

I solved this issue for dev-mode this way. maybe someone could benefit from this.

This is just a temporary solution untill Angular provides this feature in ivy i18n.

Drawback: can only be done when language files are generated to JSON :-(

polyfills.ts:

import { loadTranslations } from '@angular/localize';
import { isDevMode } from '@angular/core';

// All translation objects: must be json files for runtime-conditions! (XLF not supported)
import * as fr from "./i18n/messages.fr.json";
import * as nl from "./i18n/messages.nl.json";
import * as en from "./i18n/messages.json";


// Non-official translation loader to switch languages at runtime in development mode
if(isDevMode()){
  let translations = {};
  let lang = localStorage.getItem("lang");
  if(lang === "fr"){
    translations = fr;
  } else if (lang === "nl"){
    translations = nl;
  } else{
    translations = en;
  }

  // load translations at runtime
  loadTranslations(translations['default']['translations']);
}

Answer 2

So if you use JIT, you can use webpacks loader to hotswap language files:

main.ts

import { enableProdMode } from '@angular/core';
import { platformBrowserDynamic } from '@angular/platform-browser-dynamic';

import { AppModule } from './app/app.module';
import { environment } from './environments/environment';
import { getTranslationProviders } from './app/providers/i18n.provider';
import { LocaleService } from './app/services/locale.service';

if ( environment.production ) {
  enableProdMode();
}

const locale = new LocaleService();
locale.getLocale().then( ( localeValue ) => {
  getTranslationProviders( localeValue ).then( providers => {
    platformBrowserDynamic().bootstrapModule( AppModule, { providers } )
      .catch( err => console.log( err ) );
  } );
} );

i18n.provider

import { TRANSLATIONS, TRANSLATIONS_FORMAT } from '@angular/core';
declare const require;

export function getTranslationProviders( locale: string ): Promise<any[]> {

  // Get the locale id as arugment or from the global
  //
  const localeValue = locale || document[ 'locale' ] as string;


  // return no providers if fail to get translation file for locale
  //
  const noProviders: Object[] = [];

  // No locale or AU, doesn't require translation
  //
  if ( !localeValue || localeValue === 'au' ) {
    return Promise.resolve( noProviders );
  }
  try {
    const translations = require( `raw-loader!../../locale/messages.${ localeValue }.xlf` );
    return Promise.resolve( [
      { provide: TRANSLATIONS, useValue: translations },
      { provide: TRANSLATIONS_FORMAT, useValue: 'xlf' }
    ] );
  } catch ( error ) {
    console.error( error );
    return Promise.resolve( noProviders );
  }

}

and the local.service

import { WindowRef } from 'app/services/windowRef.service';
import { environment } from 'environments/environment';


@Injectable()

export class LocaleService {
  _locale: string;
  set locale( val: string ) {
    this._locale = val;
  }
  get locale() {
    return this._locale;
  }


  constructor() {
    this.setLocale();
  }

  setLocale() {
    const winRef = new WindowRef();

    this.locale = ( environment.countryLookup[ document.location.hostname ] || 'au' ).toLowerCase();

    const match = document.location.search.match( /au|nz/ );

    if ( match ) {
      this.locale = match.shift();
    }
    // store locale in document
    //
    winRef.nativeWindow.document.locale = this.locale;
  }

  getLocale(): Promise<string> {
    return Promise.resolve( this.locale );
  }

}

You will have to refactor it a bit to match your project, but I hope you get the gist. This might be a solution until Ivy supports proper language switching.