ngx-translate multiple i18n files

app.module.ts

export function createTranslateLoader(http: HttpClient) {
    return new TranslateHttpLoader(http, './assets/i18n/app/', '.json');
}

@NgModule({
    imports: [
        /* ... */
        HttpClientModule,
        TranslateModule.forRoot({
            loader: {
                provide: TranslateLoader,
                useFactory: (createTranslateLoader),
                deps: [HttpClient]
            },
            isolate: true
        })
    ]
    bootstrap: [AppComponent]
})
export class AppModule { }