Some posts on the Brexit thread led me to make a separate thread on this interesting topic.
My own experience with spoken language is that seemingly, if you learn another language as an adult, it is very difficult, if not impossible, to lose the accent.
I'm remembering this old workmate of mine who spoke perfect English, albeit with a heavy Puerto Rican (or Spanish, if you will) accent. His vocabulary was impeccable... his grammar was perfect... the only thing that gave him away was his thick accent.
Yet, if you learn another language as a kid, you become fluent to the point of even losing any accent. It's weird how that happens.