title: Angular 2 TranslateService detect language change
body: <p>How to detect language change in other components? My detection is made in header component. My target is to detect language change and set style.</p>
  
  <p>Child component:</p>
  
  <pre><code>import { TranslateService } from "ng2-translate";
  export class ChildComponent{
      public browserLang: string;
      constructor(private translate: TranslateService) {
          this.browserLang = translate.getBrowserLang();
      }
  }
  </code></pre>
  
  <p>Html of child:</p>
  
  <pre><code>&lt;div ng-class="{black: browserLang == 'en', red: browserLang == 'de'}" &gt;
  </code></pre>
  
  <p>Result of that is: Class is not added. If I output language string (en) is proper. But it did not listen for any changes. How to make it listen and changing classes?</p>