In Spain your employer pays, and you also pay some at the end of year. And for more complicated cases Spain publishes short instructions on how to pay taxes as an individual, just about 900 pages
I heard, Spain tax system is considered the most complicated in the world because of all the legacy stuff
I am amazed at how this is mostly not mentioned in more upvoter comments. If kei trucks were not outlawed in the US ~~for having the driver see the road too well~~ this wouldn't exist, most likely