I've been tasked to find "all the answers" regarding the SAP's extension capability.
I don't know where to start but would like to know what languages the extensions can be written in. I'd also like to know if there are fixed pre-programmed user exits or if those can be added by the programmer?
EXPERT RESPONSE
Just a small question then! SAP is extendable in very many ways. There are user exits of different technologies. It is also possible, but not terribly desirable, to modify standard SAP programs for your own ends. SAP does offer courses on enhancing SAP.
Within SAP itself, extensions will be written in ABAP. However, SAP can call and be called by external applications, and these can be written in a very wide variety of languages, like C, Java, C++, .Net etc.