In general, the Civ V Steam Workshop is notoriously bad when it comes to installing mods reliably. Note, however, that mods that include or depend on a custom DLL are not compatible with Mac versions of Civ. You can install mods onto the Mac version of Civ by following this guide. See the General Installation instructions above.You can either leave it and let the game install it for you (in which case, move onto step 3 below), or you can manually unzip the file (.civ5mod files are civ's unique compression format).
civ5mod file into your Documents\My Games\Sid Meier's Civilization 5\MODS folder.
