=> What are the languages require to build an online chat system ?

Question

I am trying to build an online chat system. what are the logic that I have to kept in mind while building this project ?

Answer 1

Java/Kotlin for Android app (if you want one).
Objective-C/Swift for iOS app (if you want one).
HTML/CSS/JavaScript for Web app (if you want one).
Literally whatever you want for desktop app (if you want one).
Literally whatever you want for back end.