This is interesting. I don't know if it's possible to adapt entirely to a new dialect or if one can change subtleties to his dialect/accent to blend in with a peer group. It's funny, though, how much we really don't know how the mind works, very interesting!
I have a few examples of what confounds me about language/dialects, etc:
During our moving sale, an older woman came to our house and my husband started to talk to her like they were old friends. This woman, to my ear, had as much of a tex-okie drawl as I do. Apparently she left Scotland at 20 something and has lived here for 50 years. My DH said it stuck out like a sore thumb. I said I didn't hear a THING!
A good friend of mine left Greece at 17 and came to the US not being able to speak a word of English. Seventeen seems pretty mature, not like a 5 year-old, in my opinion. Accept for a few words that sounded "broken" I could barely tell she was from Greece.
DH and I are fairly close to a Croatian family. They left Croatia in the 90s when their son was about 8. The son is now 26. His accent is nearly as thick as his mothers
!
We have a huge Vietnamese community here in Oklahoma City. I used to work in an area they used to call little Vietnam so many of the employees of the company were, of course, Vietnamese. Many of the ladies I worked with still sounded Vietnamese that were evacuated out of Saigon in 1974 at varying ages, while others sounded very American. Baffles me!
My DH came here to the states at age 37. He has lost a lot of his brogue, enough that when we visited 2 years ago, people wanted to know where he was from!
It's thick enough he still is told to "speak English" here in the US, but that's just ignorance.
Wondering if my oldest's son's accent will change (age 9) or if it will remain the same? We'll see!