APP_INITIALIZER.js

export function translationLoader(translateService: TranslateService): () => Promise<any> {
    translateService.setDefaultLang('en');
    return () => translateService.use(translateService.getBrowserLang()).toPromise();
}

@NgModule({
    declarations: [
        AppComponent
    ],
    imports: [
        HttpModule,
        TranslateModule.forRoot({
            provide: TranslateLoader,
            useFactory: translateFactory,
            deps: [Http]
        })
    ],
    providers: [
        {
            provide: APP_INITIALIZER,
            useFactory: translationLoader,
            deps: [TranslateService],
            multi: true
        }
    ],
    bootstrap: [AppComponent]
})
export class AppModule {
}