It isn’t a matter of learning a particular language. Beginners are always hung up on languages. Languages don’t matter! To be honest, language is not that important. You can develop fancy apps in almost every modern language.
What you need to learn to create a mobile app like Instagram or Whatsapp is how to implement a client application on the mobile device and a backend web service that the client communicates with.
Most services app will have frontend and backend part. Read more