Dave uses several programming languages. But the modding will be done in lua. Most of the code runs at least partially through lua so it won’t be too limited. But I don’t think you will get access to the parts written in c code. Lua should be easy to learn. That’s why it is often used to create the easily accessible stuff. I recommend you to make an online tutorial and one or two small scale project in lua before sapiens comes out. I think that strategy works best to learn a language. I did the same with python.
I agree that Dave’s engine is way cooler. It’s pretty specific, so I don’t know how flexible it will be, but it is cool indeed.