Set custom default fonts for Slide Masters in template files (as on Windows version)
You can set your own fonts in text boxes created as part of Slide Masters in a template. However, you can't set the default fonts for the template as a whole, as you can on Windows.
So, when someone using the template adds a new text box to a slide the font defaults to a different font (Calibri as standard).
On Windows, the option of 'Customise Fonts' is in the 'Fonts' dropdown on the Slide Master tab.
John Korchok commented
I agree, this should be added to the program interface. Until that time, here's how to create a Font Theme file using TextEdit: http://www.brandwares.com/bestpractices/2015/10/xml-hacking-font-themes/