Fun fact: that scene was mostly improvised. It was supposed to be a serious scene but Del Toro farted and so everyone started laughing. The whole persona of Del Toro's character being unintelligable was also not in the script. The lines "In English please" and "What did he just say?" and the other times the other characters couldn't understand him weren't in the script, they were genuine.

http://www.imdb.com/title/tt0114814/trivia

The character of Fenster was named after the German for window, and originally conceived as the oldest man of the group, a more seasoned veteran. Benicio Del Toro was originally asked to audition for the role of McManus. Benicio asked to audition for the role of Fenster, telling the director that he had an 'idea' for the part. The unintelligible way that Fenster spoke was Benicio's idea, and the director decided to go with it. In one scene, Hockney says in response to Fenster, "What did he just say?" That was Kevin Pollak the actor speaking, not his character; he actually did not understand what Fenster said. The cop's (Christopher McQuarrie) reaction to Fenster in the line-up ("In English please") was unscripted and unrehearsed, as was Fenster's rather strong reaction.

The line-up scene was scripted as a serious scene, but after a full day of filming takes where the actors couldn't keep a straight face, director Bryan Singer decided to use the funniest takes. A making-of documentary shows Singer becoming furious at the actors for the constant cracking-up. In an interview (on the Special Edition DVD), Kevin Pollak states that the hilarity came about when Benicio Del Toro "farted, like 12 takes in a row." Del Toro himself said "somebody" farted, but no one knew who.