Cannot set isolate: false in feature modules

I cannot set isolate: false in the feature module with extend: true.

App.module.ts

TranslateModule.forRoot({
  defaultLanguage: 'en',
  loader: {
    provide: TranslateLoader,
    useFactory: httpTranslateLoader,
    deps: [HttpClient]
  },
  isolate: false
})

FeatureShared.module.ts (lazy-loaded)

TranslateModule.forChild({
  loader: {
    provide: TranslateLoader,
    useFactory: createTranslateLoader,
    deps: [HttpClient]
  },
  isolate: false,
  extend: true
})

I have also reset the current language in TranslateService

export class FeatureSharedModule {
  constructor(protected translateService: TranslateService) {
    const currentLang = translateService.currentLang;
    translateService.currentLang = '';
    translateService.use(currentLang);
  }
}

With this setup I can load feature-wise translations files but not main (app.module) translations.