There are lots of game which are made using Unity 3d or unreal game engine. I am able to decompile an apk which is made from android studio but i don't know whether it works in those games because I don't even know from which software they had been made or which language they had been written.
Can I easily decompile them too using java decompilers or do I have to use any other method (I don't know any other method more than of java. If there is any, please tell).
By the way, and for detail, I want to decompile mad dex android game.
A decompiler for Java decompiles JVM bytecode. It has no idea what CLR bytecode (the one used by C#) looks like.
So to answer your question: no, you can't use a decompiler made for Java to decompile something that is not meant to be run on a JVM. You'll have to find a decompiler for CLR bytecode.