While not as impressive as playing competitive Scrabble in a foreign language, I thought it was fascinating in the documentary about competitive Scrabble, Word Wars[1], that one of the finalists in an American tournament was a British champion who had to keep track of which words were allowed in the British Scrabble dictionary versus the American Scrabble dictionary used in the tournament.

[1]http://www.imdb.com/title/tt0390632/