Intelligibility heavily depends on what you expect to hear, and that depends on your native language or even locality. Even a tiny amount of French accent in English makes it sound like gibberish to me (but not others, and I don't have this issue with other thick accents). I'm sure my native accent is also incompatible with someone else's ears. That's the reason people pay accent coaches.

Yes, should go without saying that intelligibly is perfectly provided it’s intelligible in whatever context you’re in

I understand the feeling, but I can usually adapt pretty quickly when someone speaks in a very unexpected accent. Sometimes I can even remember the sounds well enough that I can reinterpret it on the fly without having to ask them to repeat.

Being legible also means to cater to your audience. I work in an English-speaking company in a country where English isn't the native language, with loads of non-native speakers from around the world. Sometimes the native/best English speakers are the ones being misunderstood, because they use idioms or advanced words. None of us are bad at English, and I don't mean that I need to "dumb it down" (if anything, verbally I'm one of the worser ones), but I don't feel like I'm missing out on speaking simple with an accent.

Generalizing from my own experience, it’s easier for me to understand a non-native Spanish speaker than a native Spanish speaker and I would guess that the same applies with ESL speakers. One thing I found really fascinating is that even though I’d never studied French¹, I actually had an easier time understanding a conversation between my ex-wife and her aunt in French than when they spoke Spanish in which I was functional (my skill in the language has gone up a great deal since then so that I now read fluently, and speak and listen reasonably well, albeit less well than I would like).

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1. Thanks to my kids studying French on Duolingo and my joining them, I can no longer say that I’ve never studied it.

>Generalizing from my own experience, it’s easier for me to understand a non-native Spanish speaker than a native Spanish speaker and I would guess that the same applies with ESL speakers.

You guessed right -- it's /usually/ easier to understand other non-native speakers, both because of accent and less idioms. That is unless the accent is really heavy and doesn't match your own.

I don't think it's really to do with accent, but rather that non-native speakers tend to talk slower and use simpler grammar and a more limited vocabulary (including fewer idioms).

That does help, I’m sure. There’s also a tendency to incorrectly apply foreign grammatical structures to the language in a way that might be strange or incomprehensible to a native speaker while making perfect sense to a fellow second-language speaker.

I've read of a language, or I guess dialect of English called "European english", i.e. English as spoken Europeans that learnt it as a second language. Another example is how a Brit using too many idioms like "Bob's your uncle" would confuse English speakers that haven't been exposed to Britishisms.

Searching on YouTube just gives me this relevant result, an English that has some new/odd words that's been adapted by the Euro-bureaucrats https://www.youtube.com/watch?v=vf8KxvRYvQU

That kind of implies that there's a "correct" accent for English, even though many countries and regions natively speak it. Someone from Glasgow is just as much of a native speaker as someone from Los Angeles even though the accents are wildly different.

Hence in quotes, man

I've literally heard a story of a kid arriving to the US from Scotland and being sent to speech therapy to remove a Scottish accent.

And I've heard other such stories of American schools flagging kids for speech therapy when what they have is an accent. I feel like Americans are actually some of the worst about that.

Huh? I’m talking about my own post where I said maybe they want to feel like the are speaking “correctly” - I added the quotes because obviously what’s correct is debatable

Besides it’s not like there isn’t correct either - if you’re out in the Midwest what’s correct is just what everyone is speaking.

Its obvious that a kid from Ohio who speaks perfect isn’t going to go to Scotland and speak it “correctly”

Like it’s such low hanging fruit to always be that guy to point out the lowest level, most obvious exception

A strong enough accent can make someone impossible to understand.

I believe I have some kind of auditory processing issue because with some accents, it can be really hard for me to understand what someone is saying, when other people can understand them fine. It's gotten to the point where I avoid going to some shops in my town because I know the staff have quite strong accents and I feel embarrassed having to ask them to repeat themselves all the time

My wife has this problem. She got chided because she asked for a translator for the doctor at the children’s hospital and they just assumed she was being racist. He was Thai and his English was very difficult to understand.

Yeah, that's my concern too. I went to a beauty salon where the woman who saw me had a strong Eastern European accent, and the only fabric shop in town is staffed by people who have a strong... Indian accent? it feels like somewhere in that region. I have no problem with the people themselves, but I just struggle to properly understand their accent sometimes