Last time I was going home, I got asked to step away for an extra check, I just went along and responded in Flemish, cause that's what we speak here in Belgium, I responded with ' wat?' ik begrijp u niet, sorry'...I didn't say a word in English or Spanish nor French, for one of the agents was Haitian, they let me go after two minutes...I could understand everything they said, but it was funnier to see them look at each other in despair.
Just be polite, cooperate and play dumb, they will let you off quickly, after rolling their eyes a few times.