Nobody knows?

i can only point out this thread to you you.
https://www.concrete5.org/community/forums/5-7-discussion/what-is-th...
font managment should be easier, we all know ... this may help.
kfog

I mean setting fonts to the theme font list
see attached

The top part of the font list i have found in typography.js:

These lines seems to declare static font list

ConcreteTypographySelector.prototype.fonts = {
'Arial': new ConcreteFontFamily('Arial', 'Arial, sans-serif'),
'Helvetica': new ConcreteFontFamily('Helvetica', 'Helvetica, sans-serif'),
'Georgia': new ConcreteFontFamily('Georgia', 'Georgia, serif'),
'Verdana': new ConcreteFontFamily('Verdana', 'Verdana, sans-serif'),
'Trebuchet MS': new ConcreteFontFamily('Trebuchet MS', 'Trebuchet MS, sans-serif'),
'Book Antiqua': new ConcreteFontFamily('Book Antiqua', 'Book Antiqua, serif'),
'Tahoma': new ConcreteFontFamily('Tahoma', 'Tahoma, sans-serif'),
'Times New Roman': new ConcreteFontFamily('Times New Roman', 'Times New Roman, serif'),
'Courier New': new ConcreteFontFamily('Courier New', 'Courier New, monospace'),
'Arial Black': new ConcreteFontFamily('Arial Black', 'Arial Black, sans-serif'),
'Comic Sans MS': new ConcreteFontFamily('Comic Sans MS', 'Comic Sans MS, sans-serif')
};

Other fontnames somehow exctracted from css by javascript from file style-customizer.js
But i`ts minified and my tries to get additional fonts to those list on-the-fly by changing css failed.