Well, elive is made from bash and C, for the bash part im very in, most of the tools is made in bash, even the installer!
as an example, see all the bash programs made with:
dpkg -L elive-tools
There's elive functions for bash too, very useful, try:
el_... (TAB)
No need to read documentation, the name of the function should say everything 
When you learn how to program, you learn that good commented code is very important and it makes your code be good quality, but the best code, is the one that doesn't needs comments, in other words, "just program in english" lol
So, knowing bash is very important for everything, it is also all your terminal power so it can be the most useful language for linux
zsh is even more powerful, but is very similar and compatible with bash
So, tools like elive-multiscreens or touchpad-configurator are made in bash, knowing bash can help to improve them or to fix bugs, but is needed to know what exactly does
I would also suggest to know vim, there's a small introduction document for vim which can amaze you
C is where all the power is, the full desktop, modules, and the real power resides in C, it can be more useful for elive to know C, but C is a complex thing, because is very simple and doesn't require to learn much things, by other side requires more practice to understand it correctly lol