In ANDROID PROGRAMMING, how can we merge different languages with each other like Erlang, or Fortran? (with XML, Java & Kotlin)

Question

If Android App programming only supports XML, JAVA & KOTLIN; then how some Android apps like WhatsApp are written in Erlang and so many other languages?
Does this mean that, Java is just to create the appearance of the application or to distribute the app to the Server as well as to the client side?
Basically, then how can we merge or mix or embed codes written in other languages with each other?
If you don't know the logical answer, kindly don't just post anything and run away.

Answer 1

xml is used to create the appearance, not java. java is used for the control of the application. if it is not made in xml and java it is considered a web application, just looks good on mobile. actual android is composed of xml and java.

Answer 2

then how can certain companies use Rust or Ada or Erlang in Android programming?

Answer 3

try adding more tags to this question, I too want to know this, because I just learned a language that is supposed to be dead in 3 years