How to use translations in a Angular Ionic Toast notification

I use a notification.service.ts file that looks like this:

import {Injectable} from '@angular/core';
import {ToastController} from "@ionic/angular";
import {TranslateService} from '@ngx-translate/core';

/**
 * Stateless service that shows UI notifications.
 */
@Injectable({providedIn: 'root'})
export class NotificationService {
  isToastVisible = false;

  constructor(private toastController: ToastController, private translate: TranslateService) {
  }

  async showSuccess(message: string) {
    await this.presentToast('success', this.translate.instant(message));
  }

  async showWarning(message: string) {
    await this.presentToast('warning', this.translate.instant(message));
  }

  async showError(message: string) {
    await this.presentToast('danger', this.translate.instant(message));
  }

  async dismissToast() {
    await this.toastController.dismiss();
  }

  private async presentToast(color: string, message: string) {
    if (this.isToastVisible) return;
    this.isToastVisible = true;
    await this.toastController.create({
      color: color,
      message: message,
      position: 'top',
      buttons: [
        {
          text: 'x',
          role: 'cancel',
        }
      ]
    }).then((toast: HTMLIonToastElement) => {
      toast.onDidDismiss().then(() => {
        this.isToastVisible = false;
      });
      toast.present();
    });
  }
}

Then, in for example a page component like register.page.ts I do the following:

import {NotificationService} from '../../services/notification.service'; // on top of file

export class RegisterPage implements OnInit {

  constructor(
      private notificationService: NotificationService,
    ) {
  }

  // a service that calls an API
  async getFunctions(): Promise<void> {
    this.api.getFunctions()
      .then(async data => {
        this.Userfunctions = data;
      }).catch((error: Error | HttpErrorResponse) => {
      if (error instanceof HttpErrorResponse) {
        this.notificationService.showError(`error_service_functions`);
      }
      else {
        throw error;
      }
    });
  }

}

The key of the translation is sent here:

this.notificationService.showError(`error_service_functions`);

And gets translated via ngx-translate. The result is a multilingual toast message: