I have downloaded FontAwesome using npm and then copied the css-file and the fonts into the right folders in the root-diretory of my electron-application using grunts copy t
The Problem was in my grunt-file. I tried to reproduce the issue by simply downloading all dependencies manually at their vendors websites and placed them in the corresponding script-folder of my project - suddenly it worked.
I switched to gulp now and it still works. No idea what i was doing wrong with grunt though...