如何使用Ngx翻译翻译AngularFireDatabase？

Question

App Module.ts

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

HTML

<div class="container" *ngFor="let item of itemArray">
<div class="row">
    <div class="col">
        <p> <b>Name: </b> {{item.firstName}}</p> <---- translate First Name
    </div>

</div>
  <div class="row">
      <div class="col">
        <p><b>E-mail:</b> {{item.lastName}}</p><---- translate Last Name
      </div>
    </div>
      <div class="row">
          <div class="col">
            <p><b>comment:</b> {{item.comment}} </p><---- translate Comment
          </div>
        </div>
</div>

getDataOfFirestoreDatabase

this.itemList = this.db.list('Messages');
    this.itemList.snapshotChanges().subscribe(actions => {
      this.itemArray = [];
      actions.forEach(action => {
        const z = action.payload.toJSON();
        z['$key'] = action.key;

        this.itemArray.push(z as messageDB);

      });
    });

注意：我需要在获取AngularFireDatabase之后转换数据，例如en或fr。我该怎么办？