Which are the languages you need to know for app development , and to which depth do we know them ?

Answer 1

Depends on the platform you want to be on. If Android development then you should know Standard Java and then move on to Micro edition Java. If you're going to work with Windows then C#. Ofc Objective C and Swift is all Apple. All in all, it's going to take some time so don't even rush, just take your time.

Answer 2

is XML required for Android app development ?

Answer 3

If you want to develop Mobile App then you need to learn Android for android app development.