I've always been one to adapt an accent to those around me. Southern accent when I'm in the South, Canadian accent when I'm in Canada, Scottish accent when in Scotland, and a New York accent when I'm in New York. The accents come and go as I enter and leave those areas. Maybe not a full blown accent, but at least a notable inflection, away from my normal voice and toward that area's specific accent. Even my use of words can change a bit (saying "Cheers" instead of "thanks" when in the UK, saying "y'all" instead of "you" when in North Carolina as examples).
It seems I naturally mimic what I hear from those around me, rather than keep a constant way of speaking. It's natural for me, probably something related to my ASD, but seemingly a rare thing for anyone to do. I recall when I was very young, I found many other people more interesting than myself, so in wanting to be more interesting, I talked like those others who seemed more interesting. This would even happen when I'd watch TV shows or listen to sports on the radio, I'd start talking with an accent similar to one of the characters or commentators during the program and shortly thereafter, then resume my natural way of speaking the next day.
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DSM-5 Diagnosis: Autism Spectrum Disorder, Without accompanying intellectual or language impairment, Level 1.