要在Angular应用启动时加载翻译，需要在NgModule的providers中提供TranslateLoader和TranslateService，并在应用启动时使用translateService的getTranslation方法加载翻译文件。

代码示例：

app.module.ts

import { BrowserModule } from '@angular/platform-browser';
import { NgModule } from '@angular/core';
import { HttpClientModule, HttpClient } from '@angular/common/http';
import { TranslateModule, TranslateLoader, TranslateService } from '@ngx-translate/core';
import { TranslateHttpLoader } from '@ngx-translate/http-loader';
import { AppComponent } from './app.component';

export function HttpLoaderFactory(http: HttpClient) {
  return new TranslateHttpLoader(http);
}

@NgModule({
  declarations: [
    AppComponent
  ],
  imports: [
    BrowserModule,
    HttpClientModule,
    TranslateModule.forRoot({
      loader: {
        provide: TranslateLoader,
        useFactory: HttpLoaderFactory,
        deps: [HttpClient]
      }
    })
  ],
  providers: [],
  bootstrap: [AppComponent]
})
export class AppModule { 
  constructor(private translate: TranslateService) {
    // 设置默认语言
    this.translate.setDefaultLang('en');
    // 加载翻译文件
    this.translate.getTranslation('en').subscribe();
  }
}

app.component.ts

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

@Component({
  selector: 'app-root',
  template: `
    
{{ 'hello' | translate }}
  `,
})
export class AppComponent {
  constructor(private translate: TranslateService) {}
}