What are the languages that can be used to develop an Android application? and also which is the easiest one apart from java?

React native and ionic

its hard to get easier than java. i dont mean that to be insulting, but everything is hard to configure, find help online for, and a bunch of other bs. i'd go with java.

@calmyourtities how about kotlin?

Kotlin and Java are the two main official languages, but to use kotlin you would be better off with an understanding of Java.
There is also Javascript through React Nativr, Tabris, NativeScript where the performance is almost native and use native components for the application. Other examples include Ionic (as previously mentioned) and things like Cordova. Js is easier to some extent, but to really use it good you do need a level of profficiency with it as with anything else so don't be fooled.

There is also Python with kivy and Ruby with tools like Ruboto.

@deeaarbee you need java to use many of the libraries and when you search for a problem, the solution will most likely be in java, so youd have to convert it.

Whats about C#?

But the easiest way to go is java/kotlin. Your android application will also be more efficiently and working smoother.

C# Xamarin Android?