As for my knowledge pega is a language yet more or less a framework. But I like to describe it as a framework. Because there are no such pega codings.
Mostly the UI manipulation will do the work for us. It resides in a server.
Actually we can write SQL, Java, HTML, etc codes to support extra functionalists. That is the major connection between pega and other languages.
But adding additional language codes will be considered as violation, where you would not stick in to best practices that they have suggested.