During the 1990's, whilst in Chile, I saw a TV news item that caused a great deal of concern at the time. They broadcast the recording of a conversation between a South American pilot and control tower. Tower; "Flight XXXX you are on a collision course, make IMMEDIATE right turn". Several seconds later the pilot replied; "Que?". The controller then repeated the urgent warning, this time in Espanol. Obviously, the incident illustrated the importance of pilots being able to speak English!