Basically I'm wondering if there is a concise way to represent the loss of understanding a foreigner would experience if they were to encounter an American idiom for the first time.
An example: http://www.youtube.com/watch?v=gjwofYhUJEM
closed as off topic by Robert Cartaino♦ Dec 3 '11 at 2:30
Questions on English Language & Usage Stack Exchange are expected to relate to English language and usage within the scope defined by the community. Consider editing the question or leaving comments for improvement if you believe the question can be reworded to fit within the scope. Read more about reopening questions here. If this question can be reworded to fit the rules in the help center, please edit the question.
As far as the question in the title of your question, I believe the word you are looking for is idiom.
And what the foreigner would experience, your word is likely confusion.