Despite having spent some considerable time in the States, and learnt to decode most regional communications (the first time we landed in Atlanta Geeowja was a bit of a strain, y'all) I never learnt to speak it. Possibly because the people I met made an effort to understand British - nay, English English (we had a Glaswegian with us who had considerably more problems, but we had difficulty following him, let alone the Texans). I haven't learnt any Dutch or Danish, either - I'm not much of a linguist.
But when I wrote a story for an American publisher (that is, one who resides in the US of A, not merely from the double continent), though it came back several times for editing the instructions were 'dumb it down. Simplify.' never 'Americanise' (just as well, really, as I doubt if I could have done so). The American publisher underrates his readership's intelligence and education level, not their linguistic skills.
I do not recommend 'mid-Atlantic' (we used to do films dubbed in it for firms such as Firmenich and Rolex, and all it does is annoy both sides of the pond) nor the 'international English' growing, particularly in the extreme orient - I figure that a language which can be accommodated from Yorkshire to Cornwall, and from Maine to Louisiana is flexible enough to allow for a few more dialects.
