Translate do not work in constructor for translations added in json files

[ihd2911]

Current behavior

constructor(
    private translate: TranslateService,
    private titleService: Title,
  ) {
    console.log('in');
    translate.setTranslation('en', {
      //HELLO: 'helloa '
    });
    translate.get("HELLO").subscribe((newTitle: string) => {
      console.log(newTitle);
    });
}

If i uncomment "HELLO: 'helloa '" translation starts working. If i comment it and same translation in i18 folder in assets folder, it stops working. It do not work only in constructor, where as translations work properly at other places

Environment

ngx-translate core version:9.1.1 
ngx-translate http-loader version:3.0.1
Angular version: 5.0            

[ihd2911]

Duplicate of #758