I had a friend in med school who would study her neuroanatomy in an English accent, just to help it stick out better for memorization. (She passed with flying colors, so I guess it worked!)
That was different.
Foreign Accent Syndrome is an extremely rare problem (0nly sixty cases ever reported) caused by head trauma or stroke, affecting the speech areas of the brain.
Sufferers do not suddenly pick up a new language, only what appears to be the accent of another culture using their own native words. Idioms are not picked up (so my cartoon is a bit off, sorry). In fact, the pronunciation of certain letters and vowels are off enough to make the listener think they are hearing a particular type of accent.
A brief search told me this hasn't been seen prominently in any novels. This one is truly up for grabs.
In any case, this is yet another example of how remarkable the brain is and what unusual things occur when the wiring goes awry.