I had a Welsh work colleague years ago. A few times he was on the phone and spoke Welsh. None of the mental markers on what language he was speaking seemed to change. It sounded like English, spoken with a Welsh accent. Until my brain tried to interpret it. It was like I had had a stroke. It parsed as English, but wouldn’t make sense. It took a conscious effort to remind myself that he wasn’t speaking English.
The film hot fuzz has an amazing take on this. They need to talk to a farmer, but end up bringing the dog handler along. It turns out it’s not for the dog. It takes 2 accent translations to make sense of what he is saying!
https://youtu.be/Cun-LZvOTdw