The Tools > FME Options > Translation > Python Interpreter setting should be there on a Mac. However, it's at the foot of the dialog and the scroll bar might be invisible! I see a screenshot from a colleague where he can't see it and he says "silly Mac OS with their invisible scrollbars".
Does that help?!
I have the 2015 version, did it change location? Or am I looking in the wrong toolbar.
While I have the 2016 version, I believe it is the same in 2015: FME Workbench > Preferences... > Translation > Interpreters. If You have a smaller screen (for example a macbook) and invisible scrollbars, it can be very hard to find!
To install multiple python modules using the method described
mentioned here, you have to call the fme command line tool, which is default on the mac at /Library/FME/<your fme version>/fme. The simplest way is adding it to your path:
export PATH=/Library/FME/2016.1:$PATH