platform.setLang()

Hello!
I’ve read about platform.setLang() method as i understand it should change “lang” attribute in index.html.
So, here is my code:
app.component.ts

@Component({
  templateUrl: './app.template.html'
})
export class MyApp {
  rootPage = FirstRunPage;

  @ViewChild(Nav) nav: Nav;

  constructor(
    public platform: Platform,
    public translate: TranslateService,
    public config: Config,
    public statusBar: StatusBar,
    public splashScreen: SplashScreen
  ) {
    platform.ready().then(() => {
      this.statusBar.styleDefault();
      this.splashScreen.hide();
    });
    this.initTranslate();
  }

  initTranslate() {
    this.translate.setDefaultLang('en');
    const browserLang = this.translate.getBrowserLang();

    // >>>>> Subscribe to onLangChange event and update platform lang attribute
    this.translate.onLangChange.subscribe((params: LangChangeEvent) => {
      this.platform.setLang(params!.lang, true);
      console.log(params!.lang);
    });

    if (browserLang) {
      this.translate.use(browserLang);
    }

    this.translate.get(['BACK_BUTTON_TEXT']).subscribe(values => {
      this.config.set('ios', 'backButtonText', values.BACK_BUTTON_TEXT);
    });
  }

}

In console i see correct value in “params!.lang”, but inside ChromeDev tools lang attribute stays as it was.
Can someone clarify what may be wrong here?

“ionic-angular”: "3.9.2"
Chrome 64.0.3282.186
Windows 10 pro (1703)