The concepts still roughly translate and help, though. You have projections/mappings in FP. Or if you want to go deeper, recursion. Understanding loops before those will definitely make them easier since they are equivalent.
The argument that learning a second language is as difficult as learning the first doesn’t really hold water in practice as well, lots of people have done so.
I'm not saying there are zero differences or that $other_language never has any new concepts to learn, but in functional languages variables are still variables, functions are still functions, conditionals are still conditionals, etc. Important aspects differ, but the basics are still quite similar as is a large chunk of the required reasoning and thinking.
