ng2-translate:有没有办法在缺少翻译的情况下使用默认语言？

import { NgModule } from '@angular/core';
import { BrowserModule } from '@angular/platform-browser';
import { TranslateModule, TranslateLoader } from 'ng2-translate';
import { TranslateStaticLoader } from 'ng2-translate/src/translate.service';
import { AppComponent } from './app.component';

export function createTranslateLoader() {
  return new TranslateStaticLoader('./assets/i18n', '.json');
}

@NgModule({
  imports: [
    BrowserModule,
    TranslateModule.forRoot({
      provide: TranslateLoader,
      useFactory: (createTranslateLoader)
    })
  ],
  declarations: [AppComponent],
  bootstrap: [AppComponent]
})
export class AppModule { }

import { Component } from '@angular/core';
import { TranslateService } from 'ng2-translate';

@Component({
  selector: 'app-root',
  template: `
    <h1>{{ 'HELLO' | translate }}</h1>
  `
})
export class AppComponent {
  constructor(private translate: TranslateService) {
    // 设置默认语言
    translate.setDefaultLang('en');
    // 加载其他语言的翻译文件
    translate.use('fr');
  }
}