Having the same problem, even though it'd been fixed for ages on PC, Aspyr didn't bother with the fix, and broke the Mac version after the PC fix came out.
I haven't tried applying the fix yet, but if the Windows version of the fixed Lua script will work on Mac, the place to put it would be in (note that ~ signifies your home directory): ~/Library/Application Settings/Steam/SteamApps/common/Sid Meier's Civilization V/
...at that point, you have to go into the app, the name varies based on the version of the game you're using, in my case, it's "Sid Meier's Civilization V: Gods & Kings", yours may have "Brave New World" after the colon, or nothing if you're running vanilla. If you're using Finder, you'll have to right-click the app and choose "show package contents" to go into the app folder.
The rest of the path is contents/home/assets/UI/FrontEnd, so, for G&K, the full path would be ~/Library/Application Settings/Steam/SteamApps/common/Sid Meier's Civilization V/Sid Meier's Civilization V: Gods & Kings/contents/home/assets/UI/FrontEnd
If you try replacing it, I highly recommend making a backup first, as, if Aspyr have had to tweak it for the Mac version, replacing it could make things worse, so that even new games won't work correctly.
If using finder to move the file, you may also need to show your library folder, which is hidden by default in Lion and Mountain Lion. To do so, type "chflags nohidden ~/Library/" into a terminal (/Applications/Utilities/Terminal).