Re: APL - without a shadow of doubt.
"I have a knack for picking up languages quickly, which meant that I’d often have to pitch in on eclectically coded projects. APL tested my abilities and patience and - although I got to be reasonably adept at it - I never want to touch it again."
This is actually pretty common. People who already know programming tend to have a difficult time picking up APL, but people who have never programmed at all tend to pick it up fairly easily. Understanding how the computer itself works makes it difficult to cast aside habits dealing with linear, sequential strings of instructions. What APL does well is allow mathematical ideas to be expressed without going through that 'how does a vector get processed?' step that most of us in this forum cannot ignore.
I freaking love APL. I use it as my desk calculator app. I'll never be any good at it because I've spent too many years thinking in Fortran/C/assembler/Pascal, etc., but I'll keep trying, because it rewards, maybe even forces, thinking outside the box.