Enough that the default assumption should not be the USA just based on English.

There are enough other tells, such as saying that something is legal or illegal without giving a jurisdiction, or the imperial system (for things that don’t describe a person’s dimensions- I’ve rarely heard Brits describe their weight in kilos and I’ve never heard anyone outside of the commonwealth use stones except as a joke). Even things like budgeting student loans or medical bills as a huge expense or talking about long driven commutes.

It’s not perfect, but it’s more accurate than just using English. How many German speaking users do you encounter on Lemmy speaking English (it’s obviously not just German, but I recognize your username from the German speaking communities, so it’s an example I hope will work) whom you only recognize as German speakers through their username (either through familiarity or the language of the username)? I encounter it all the time. I also occasionally see two users interacting with a thread in general in English, but with each other in a different language because they recognize each other as speakers of that language, even though I would not have pegged either of them as a resident of a non English speaking country without their mutual interaction (obviously speaking any given non English language doesn’t mean you’re from or reside(d) in a country which officially uses that language, but it’s a pretty big indicator, especially for languages with fewer speakers than the top ten)