Make sure the have a english verion available, as a print or something. So no confusion is given around the card that is played. I remember a nasty situation at a European event in 2008 where Madg0blin had english cards and his opponent German ones. The rules said that is you used cards with another language, you should have the english version available. Madg0blin however isn't too good in german, especially the less known cards gave trouble, and his opponent didn't know english. His opponent got a timewin, and that led to a debate. It wasn't fun and spoiled it for Madg0blin, who followed the rules of the tournament.