Airbnb's Secret Tool for Designing for Every Person on the Planet
That increases the number of screens Airbnb needs to take into account to 2,400 - and that's before you multiply for the vast array of screen sizes on the market today, or consider in-progress versions of coming app updates, or how an Airbnb host's site looks when viewed by someone in a different language.
By the time you're done with the math, Airbnb doesn't have 12 or even 2,400 screens to design for.
It has exponentially more than that, like all the possible moves in a game of chess expanding to surpass the number of atoms in the known universe. It's a huge amount of variables to keep track of, not just for designers but for quality assurance.
When you have this many possible permutations of screen sizes and languages, how can you possibly guarantee that your app design works on every single device?