Do you think that one factor is that if aspies tend to have difficulty communicating, even in their native language because of not getting NT nuances and social cues, they have been compensating by working incredibly hard at the bits they can get, i.e. the basic vocabulary and pronunciation?
If this is true, then it means these individuals are already used to really, really trying to listen, learn and replicate language, which would lead to someone who takes for granted the work involved in picking up a new language.
I ask this because I apparently have semantic pragmatic language disorder, which no one noticed for over 3 decades, I don't understand people most of the time, but yet when going abroad in a group, or meeting foreign people at home, I am the one in the group who tries the hardest to communicate with the foreigners, and am noticeably very good at basic communication, where the other party isn't trying to play head games.