Chat app how???,,

Question

How can I create a simple chat app like WhatsApp??
What are the requirements?
What are the language I need to use?
Etc etc.....

Answer 1

Which language did you want to gow with kotlin or java

Answer 2

There are plenty of ways of doing it, with a variety of languages. If you want an "easy" way to do it go over to socket.io and read about it to understand how it does communication. Search online for tutorials to help you if you need.
I can personally say it's simple to use and manipulate to make a simple app or a complex one. The one I made was with Cordova to make the app, then made a server. The programming was made in js like a website.

But that's one way of doing it, there are a lot more, and you could even do it without something like socket io, projects like it just make things easier.