如何翻译使用ngFor标签？

Question

    <mat-form-field>
    <mat-select multiple name="Amenities">
  --->  <mat-optgroup *ngFor="let itemName of amenitiesGroup;let i = index;" translate [label]="amenitiesTranslateName.{{i}}.item">
    <mat-option *ngFor="let amenities of itemName.amenities;let i = index;" [value]="amenities.value">
    </mat-option>
    </mat-optgroup>
    </mat-select>
    </mat-form-field>

注意：我需要使用mat-optgroup转换标签数据