translation-loader.service.ts

export class TranslationLoaderService extends TranslateLoader {

  constructor(private http: HttpClient, private moduleName: string) {
    super();
  }

  getTranslation(lang: string): Observable<any> {
    return forkJoin({
      moduleTranslation: this.http.get(`/assets/i18n/${moduleName}/${lang}.json`),
      commonTranslation: this.http.get(`/assets/i18n/commons/${lang}.json`))
    }).pipe(
      map((translation: { moduleTranslation: any, commonTranslation: any }) => Object.assign(
        {},
        translation.commonTranslation,
        translation.moduleTranslation
      ))
    );
  }
}