I know this forum is mainly intended for the the U.S, but I’m wondering what kinds of things in aviation usually vary from country to country?
The only things that really vary significantly are the licensing and training requirements which is why we don’t give much advice to foreign pilots. As far as the flying goes fortunately most (if not all) First World countries operate under ICAO (International Civil Aviation Organization) rules. This allows someone like me, who’s done all his training in the US, to fly to virtually any country safely and not get in trouble. Probably (in my mind) the biggest issue is the language barrier. While English is the official language of the ICAO and therefore is the only language used on the radio accents do come into play which is why proper phraseology is so important. Pilots in the US are actually the most lax in this area since we all understand each other pretty well. Overseas they’re much more exact and particular. The only other thing that comes to mind is in China and Russia they use meters instead of feet for altitudes but most aircraft simply have a button you can press to display either.