订阅方法不会对更改做出反应[Angular 2]

I've got the method in my app.component that changes languages in my LangService. When the change occurs the LangService should then response with Observable object to all my other components as I have subscribed to changes in all my components. Unfortunately, it's not happening. It only response to the app.component that called the function for changing the language. I'm not sure where I have made a mistake. Maybe I'm just misunderstanding the whole concept as I'm new to Angular. I've got the method in my app.component that ch