Oh, right! And you think DirectWrite would not be available in GTK? (I am absolutely not familiar with GTK for Windows.)
Good hint, I compiled Geany with GTK+ v2 on Linux and ligatures work: ![image](https://user-images.githubusercontent.com/6584443/85866030-13fdda80-b7c7-11e...)
So it's not a GTK+ v2 vs. v3 problem per se.