Originally Posted by
liaa
As far as I've encountered (I'm writing this on a mac myself) macs use .MPQ files in the same way Windows does. I can't see any reason why en/gb clients would differ either.
Ensure you have your file in the \Wow\Data folder, named something along the lines of Patch-X.MPQ where "X" is any number from 5-9 or any letter. I would avoid using "4" as this has caused problems with myself and others with Blizzard patches.
While this has not been a problem recently on Windows machines, make sure .MPQ is capitalized. It used to not work if it was lowercase in windows, perhaps the problem is still there on macs.
Best of luck.