which is the best machine language for android app development?

Answer 1

Kotlin.
https://developer.android.com/kotlin/get-started.html

Answer 2

if you want to try ready to use APIs for Android development then you should get tensorflow API they have an example build for machine learning you can also try it on your phone by just downloading the Android example from their gihub repo. Good luck!
And for the language you should use either Java or Kotlin or JS interpreted down to Java

Answer 3

somehow everybody uses Kotlin ( I see the advantages), although I prefer Java. but you can basically write in any language (at least that is what I've heard, but Android Studio only works with kotlin, java.