As an American, it’s always a bit startling to realize that “German,” “French,” “Italian,” etc. are in many ways hugely diverse language families with dialects that are often not intelligible by all speakers (as opposed to English where, with a few extreme exceptions, there’s not really a problem with mutual intelligibility and the written language elides most of those distinctions).

I don’t have enough broad knowledge of Spanish (Castellano) to comment on its intelligibility across dialects (although Argentine/Uruguayan Spanish is more of a challenge to my Mexican-Spanish trained brain than European Spanish).