What should one learn in order to be an app developer ?

Answer 1

Depends on what device you are talking about. For Windows apps, you should start with C#, for Android you should learn Java, for Apple devices: Swift, and for Linux apps: C, C++ or python, and finally for web apps: html, css and everything related to JavaScript

Answer 2

Assuming you're talking about mobile apps, Java or C# should be enough.

@AMHAUAL Amar You are not a real programmer until you have mastered INTERCAL

Answer 3

Everything.Every Possible langauges and Mastering in all of them,Them You will be a Programmer.