What language should I learn if I want to create Android apps?
The primary language used to create Android apps is Java. Additionally, you may also use Kotlin, which is a more modern and concise programming language that is fully compatible with Java and is becoming increasingly popular among Android developers.
What are Kotlin's features?
Kotlin is a statically typed programming language developed by JetBrains for the Java platform. Some of the main features of Kotlin include:

Interoperability: Kotlin is fully interoperable with Java and can be used seamlessly with existing Java code.

Concise and expressive syntax: Kotlin has a concise and expressive syntax that allows developers to write code more efficiently and effectively.

Null safety: Kotlin has built-in null safety features that help prevent common null pointer exceptions in Java.

Extension functions: Kotlin supports extension functions, which allow developers to add new functions to existing classes without having to inherit from them.

Higher-order functions and lambdas: Kotlin supports higher-order functions and lambdas, which allow developers to write more concise and expressive code.

Coroutines: Kotlin includes support for coroutines, which are lightweight threads that allow for more efficient and expressive concurrency.

Data classes: Kotlin provides support for data classes, which are classes specifically designed for holding data.

Type inference: Kotlin has a powerful type inference system that can automatically infer the type of variables and expressions, reducing the amount of explicit type information needed in the code.

Annotation Processing: Kotlin includes an annotation processing system that allows developers to generate code and metadata at compile time.

These are just some of the main features of Kotlin, and there are many more that make it a powerful and versatile programming language.