Great question! 'Break a leg' comes from theater, where the superstition is that wishing an actor good luck before he goes onstage is actually BAD luck... so to encourage him you wish for his injury. Another show biz (business) phrase for this is: "Knock 'em dead!" (knock them dead) which means to 'knock out' (= impress, from boxing i guess) the audience "Give 'em hell!" is a general term of encouragement especially to someone entering a conflict, I seem to remember someone in WW2 saying this, but it's probably older. "Best of luck" is too formal to actually say aloud much but it makes good writing in a letter or greeting card, or when signing a yearbook. During WW1 a common phrase among soldiers in the trenches before going into battle in which they might likely be killed, was "Over the top and best of luck to you." The interesting thing is that 'best of luck to you' also has become a phrase which means 'good luck and go away'. For instance if someone on the street is trying to tell you their story, you cut them off with a little blessing. It's actually similar in the Muslim world "God help you" (because I'm not going to)

well ,we don`t beleive about the luck because we beleive with Act of God so no need for say good luck !! but we have in my language which it`s arabic language words for that . we say "hadan moowfak " or "bltafweek".

in italy we say "in bocca al lupo" but in calabria the region in which i live we say also "in culo alla balena" that means more or less "in the ass of a whale" eheheh

祝你好运~ zhu2 ni3 hao3 yun4

in canada, we just say "good luck" or "break a leg".