It's a speech impairment. They're relearning how to form words. Just because one culture forms a rhotic R one way and another culture forms it another way or even deprecates it doesn't make you speak in their accent.
Myabe a bit pedantic but I've always disliked this "my husband spoke French after his stroke" thing.
I admit .. "like Steffi Graff" signals how it sounds, at least to somebody. My friends with stroke speech impairment spoke like they'd had dental local anaesthetic, or were talking through a mouthful of marbles. It's as if they had lost control of some of the finer grained muscles related to speech and had the gross motor skills for the breath, the vocal cords, and the jaw only.
She calls it "her German," BTW.
PS I should add there are quite a few different types of aphasia. The case in the article seems uncommon.
They would talk about the bird songs from outside but being asked if they wanted a coffee would freeze. Thankfully they made a full recovery after a few months.
That happened (and still does) with my second language, absorbed mostly through immersion/native exposure on a day-to-day basis.
When I go into that language mode and am having a conversation, my brain can pick a word and speak it, and I have no idea where I learned it, or even if it was correct? It will immediately sound strange and "unknown" to me. I would struggle to define the word, and if it was spoken to me I probably wouldn't understand it. It just felt correct to fit it there in the conversation.
Then I google translate it and find out "huh, yeah, that was actually correct and completely appropriate in that context".
It's so strange.
When his butler asks him a question he says “Pardon, no hablo espanol. Uno momento! Mucho hablo espanol!”
It’s similar to that. You surprise yourself all the time.