Because most people in the Western world do speak it proficiently. As well as the more urban populations of much of Asia.

I live in the Netherlands, where it's not the Americans assuming everyone speaks English. Sometimes it's quite bizarre too: we have this deaf, Ukrainian colleague who doesn't speak but communicates with Russian Sign Language (and whatever gestures you can think up on the spot), and it's very blatant that he doesn't speak English because he doesn't speak and can't hear, and has never written any notes in English or anything like that, but I've still caught other colleagues mouthing, or sometimes outright saying, things to him in English, as if it'd help. I remember once coming across a mute man who obviously understood Dutch, who then tried to ask someone a question, who then replied in a very "my husband is antiquair" kind of way. Otherwise it's mostly European tourists and immigrants who assume you speak English.

Because we have to if they don't speak our language

PLEASE don't COMPLAIN about my THAI at a TOURISM HOTSPOT

I say it because every time I try to speak in someone in their language, they immediately switch to English. (even the one I'm pretty damn good at)

Because of the dominance of English, many people learn it and that's enough to talk to people from many countries, but what are we supposed to do? We can't learn all the other languages.

Why’s everyone assuming this isn’t in America? I’ve seen signs like this here and it’s immigrants’ way of saying “listen we’re trying to speak your language well, but please be sympathetic as it’s our second (or more) language”. We’re generally fine with people not speaking English when we’re outside America, it’s inside our borders that we’re tremendous assholes about it

Classic mistake of someone Thai trying to speak English. They forgot to write the words “long time” at the end.

Hop on a 6 hour flight, or drive for 40 hours from most countries and you’ll likely find yourself in a place that speaks an entirely different language. In America all that gets you is someone who has a different kind of twang in their voice.

Not saying it’s right to make that assumption but it’s definitely understandable why people do.

I wonder if there was a time in which a similar sign was written in Latin.

Of course as people pointed out, this is far from a uniquely American thing. Also, I'm sure by American they mean the USA, but "Americans" are inclusive of north, central and south America. Here in Europe, we also expect people to speak English as it is the universal language.

As a side note, it is also often commented that Americans (USA Americans) can only speak English. This is a narrow view that primarily broadly looks at white Americans and ignores the fact that the US is a huge melting pot of cultures and for many US citizens English is their second or third language.

It goes without being said, the contents of the picture should never have a reason to be written. Don't be a dick to people trying to help you.

I've been to Thailand. It's not the Americans that are complaining, it's the British and the Australians, both of which also speak English.

Why are you jumping to Americans?