async translations angular 6

main.ts

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

import {AppModule} from './app/app.module';
import {environment} from './environments/environment';

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

fetch('/api/test.de.xlf')
.then(res => res.text())
.then(translations => {

  platformBrowserDynamic().bootstrapModule(AppModule,
    {
      providers: [
        {provide: TRANSLATIONS, useValue: translations},
        {provide: TRANSLATIONS_FORMAT, useValue: 'xlf'},
      ]
    })
    .catch(err => console.log(err));

});