TypeError: Cannot read property 'subscribe' of undefined (Angular Unit-Test)

I have a simple test that is structured like this:

import { async, ComponentFixture, TestBed } from '@angular/core/testing';
import { BreadcrumbsComponent } from './breadcrumbs.component';
import { RouterTestingModule } from '@angular/router/testing';
import { TranslateLoader, TranslateModule, TranslateService } from '@ngx-translate/core';
import { HttpClient } from '@angular/common/http';
import { HttpClientTestingModule } from '@angular/common/http/testing';
import { BreadcrumbsService } from './breadcrumbs.service';
import { multiTranslateHttpLoaderFactory } from 'app/app.component';

fdescribe('BreadcrumbsComponent', () => {
  let component: BreadcrumbsComponent;
  let translateService: TranslateService;
  let fixture: ComponentFixture<BreadcrumbsComponent>;
  let translateServiceStub: Partial<TranslateService>;


  translateServiceStub = {
    getBrowserLang() {
      return 'de';
    },
  };


  beforeEach((() => {
    TestBed.configureTestingModule({
      declarations: [BreadcrumbsComponent],
      imports: [
        RouterTestingModule,
        HttpClientTestingModule,
        TranslateModule.forRoot({
          loader: {
            provide: TranslateLoader,
            useFactory: multiTranslateHttpLoaderFactory,
            deps: [HttpClient]
          }
        }),
      ],
      providers: [
        {provide: TranslateService, useValue: translateServiceStub},
        BreadcrumbsService
      ]
    });
    translateService = TestBed.get(TranslateService);
  }));

  beforeEach(() => {
    fixture = TestBed.createComponent(BreadcrumbsComponent);
    component = fixture.componentInstance;
    fixture.detectChanges();
  });

  it('should create', () => {
    expect(component).toBeTruthy();
  });
});

Currently this error is thrown, which I just can not handle:

TypeError: Cannot read property 'subscribe' of undefined

This is my class and the one line in the ngOnInit method causes this error:

export class BreadcrumbsComponent implements OnInit {

  breadcrumbs: Breadcrumb[] = [];

  constructor(private router: Router,
              private activeRoute: ActivatedRoute,
              private translate: TranslateService,
              private breadcrumbsService: BreadcrumbsService) {
  }

  ngOnInit() {
    this.translate.onLangChange.subscribe(() => this.identifyRoute());
  }

...

What am I doing wrong here? Or. Is there a way to get around the error or to mock this line so that the test goes through? I really have no idea how to mock this line in my test.