From the perspective of the learner, the actual cognitive work to get to mastery is of a similar order of magnitude and similar nature. The feature crossover is probably 80-90% depending on how you choose to enumerate them.

The question was about that, specifically, not about the history, not about the nuanced details of who created it, but about how hard it was to pick up.

Specifically "Any recommendations on how to learn it"

It's not in the class of R, FORTH, assembly or Haskell. It's not like Erlang. It's as conceptually approachable as Basic and historically was taught after Basic to tens of millions of people over the course of two decades, in that order.