Introduction to PHP
I was once asked to help out an affiliate at an old employer.
The affiliate's code was in PHP which I'd never used before but I was able to understand enough to find numerous errors in a few hours and fixed it for them. Typical offshore code written with assumptions and no thought of "what would happen if?"
Like most languages I know now, I picked up enough in a few hours to understand the code but like a golfer, I'll spend the rest of my life actually trying to be good at it.