The only thing I had issues with personally (after doing some Google Translate of the most legalese words) was one of the last fields, "capacity in which acting"... which was a freeform field instead of a dropdown menu. I just winged it and wrote "individual" (since I'm planning to file my indie game income as "hobby" when doing my swedish taxes next year, which seems to be the most appropriate given my circumstances), but it really was the final straw in my impression of that thing's UX. I mean, if there's only a set number of possible capacities in which you can act, why NOT have those be the only you can choose from? Being forced to guess whether what you're writing is a valid answer or not is pretty frustrating.
I've heard that there's a big industry in the US that exclusively makes tax form support software, and which are lobbying a lot to keep the paperwork as convoluted as possible so they can keep making money... not sure if it's true or just a conspiracy theory, though.