What is the simplest programming language I can use to build an android mobile application?

Before Language you know to know the Android Application architecture. They i think JAVA is the easiest language for you to develop the Apps. Good Luck :)

have to use java programming language 

It is easy to say that there is no way to develop an android application without java . Java is the core of the android development  , But infarct there are a couple of websites that allows you to build your android application with least  basics programming skill or without any programming skills . some gives you the source code ( mostly paid ) others free without the source code such as appyet

But again In order to build such a professional application you need to learn java from the basics .  

Java XML is best and simple language to built android app

To build an android mobile application you can use Hybrid application, the development is faster, simpler, more rapid and the application is easier to maintain....You can get started today with knowledge of HTML, CSS and JavaScript. Hybrid applications are web applications (or web pages) in the native browser.

I think that there is only one language to build android mobile application, it is Java...

But now there is a lot of IDE for programming Android app like eclips and you can choose from them.

First of all , U need to have the basic knowledge of java to build an android mobile application. Java is very essential and it is simple also.

too , You may use action script3 with  adobe flash after version sc5

it"s very easy for you 

good lock

Java using Android Studio may be a good choice for you to build an android mobile application