My accent reduction coaching clients frequently ask me how foreign actors are able to speak with an American accent.
One theory that I have is this: many of the foreign actors who learn to speak with a very authentic American accent are from England, Ireland and Australia.
Since English is their primary language, they already use the correct syllable stress, word stress and intonation.
Syllable stress, word stress and intonation are speaking skills that actors from continental Europe, Asia and South America & Africa need to learn.
Here’s a great story by a Spanish actor and journalist that explains how difficult speaking with an American accent can be in the world of entertainment.
There are actors from places other than England, Ireland and Australia who speak with an impeccable American accent. These people include Marion Cotillard and Julie Delphy (both French) but I think they’re the exception, not the norm.