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.