Color me skeptical. Just how authentic are these accents, anyway? Is that woman speaking with a real Chinese accent, or what English-speakers think a Chinese accent sounds like? Did they ask any genuine Chinese immigrants what they think about her new speech patterns?
Accents, of course, are relative; everybody insists they speak their native language “without an accent.” I was born and raised on America’s east coast, and speak what I consider “unaccented English,” but if I went to Britain everyone would say I have an “American accent,” and in America’s Deep South I have a “northern accent.”
When you say someone speaks your native language with an accent, what you actually mean is that they pronounce it differently than you. And there’s two basic types of differences: sounds from your language which foreigners cannot pronounce, and sounds in their language which you cannot pronounce. (If you, a native English speaker, are talking to someone who speaks with a German accent, there’s a good chance the German cannot produce the “th” sound, but can sound certain gutturals which your English-speaking self can’t replicate.)
So, for these people who get brain damage and wind up speaking “with foreign accents”: how much of that is “sudden inability to produce common English sounds” versus “sudden ability to pronounce non-English sounds?” That Englishwoman who developed “a French accent” – did she suddenly wake up with the ability to accurately pronounce French nasal vowels, or is she speaking more like “Zank Evan for leetel guhrlz?”
I once saw an episode of Graham Norton’s British talk show, where Norton found some American tourists in the audience and had them spend time backstage with a British vocal coach to learn how to pronounce certain phrases while sounding “British” rather than “American.” So he brought out the Americans and had them say sentences that repeated certain vowel sounds. To my American ears they sounded authentically British but, judging by the laughter of the British audience, I gather a real Briton wouldn’t be fooled for a second. Nor do I think I could do any better -- a Briton would likely say I have an “American accent” regardless of how I try to talk, because I’m apparently incapable of pronouncing certain words “the British way.” (Indeed, that episode of Graham Norton suggests I’m not even capable of hearing the difference between “a genuine British accent” and “an American trying and failing to replicate one.”)
My point is, I don’t find it surprising that certain types of brain damage can result in people suddenly losing the ability to “properly” pronounce words according to the standards of their native accent, but I highly doubt they are actually replicating an authentic “foreign accent” relative to their native one.