Funny story, had this happen to me in a hostel in Germany. I had to “translate“ from English with a heavy Italian accent to/from English with a heavy Vietnamese accent between roommates. Basically I just repeated what each said into my California English accent with a few touch ups. Everyone finally understood. :D

Same thing happened to me once with a Welsh couple in Krakow. The husband and I could understand the wife but not each other.

I did the same for my Grandfather, with his Punjabi accent, and a Jamaican cashier.

Spot on. I've witnessed Chinese and Indians (all with decent English skills) be unable to conduct business meetings due to difficult understanding each other's accents. On that project, I frequently 'translated' from English to English, with little/no change in word choice or sentence structure.

I've had to do the same thing in a work context as well, it was eye opening for me.

> Meanwhile, I’ve seen e.g. Mexican and Chinese ESL speakers have very bad mutual intelligibility, because they make very different mistakes.

That's true. Assume a monolingual learner. You can predict the kinds of mistakes they will make based on their native language (phonetical, phonological, semantic, etc.). As a person learns more languages, they will likely get better at decoding these things. Particularly cultural based assumptions used in languages.

Immigrants in Japan have the same experience too. We often make the same mistakes and thus have a shared understanding of misunderstandings. I would expect immigrants in other places appphave similar experiences too.

A friend of mine spent a few months in Japan, and he said the strangest part was learning that speaking simple, slower English with a strong Japanese accent was often better for getting around than using his broken Japanese.

That’s not surprising. I myself have a lot of trouble understanding the way some foreigners speak Japanese because of the mangled pronunciations.

One of the fun exchanges I saw transcripts in a linguistics course was between two ESL speakers - one native Spanish, the other native Japanese. Something as simple as not knowing the word “income” and using the Spanish “ingress” which was interpreted by the Japanese speaker as “English” was like the Naked Gun of language comedy for me.

But as an ESL person myself I’ve never thought of English as a language about rules as much as memorizations. It’s the x86 of human languages, for better or worse, and trying to systemize it fully was how I messed up English most as a kid and how my parents tried to teach it to me.