The most difficult esoteric programming language is not Brainfuck. It is Malbolge:

"It took two years for the first Malbolge program to appear. The author himself has never written a Malbolge program. The first program ["Hello World"] was not written by a human being; it was generated by a beam search algorithm (...)"

(https://en.wikipedia.org/wiki/...)

So basically it took a brutforce try-and-error approach to write "Hello World". Absolutely crazy! Imagine malware written like that 🤖