is it so hard to learn .lua ?

Lua is probably on the easier side of programming languages. If you are an avid source fan it is very good to pick up so you can make content yourself rather than leeching.

I recommend firstly looking at the documents online and read them all. Then, go to some simple (smaller) plugins and see how all the files work line by line. The language is pretty self-explanatory.

All it really takes is commitment, like all code, and it takes time. You might avoid doing it and try to find shortcuts but training someone to do it but everyone eventually learns just by spending a bit of time.