Here there's a search for a base font :
https://github.com/pure-data/pure-data/blob/master/tcl/pd-gui.tcl#L468
Here there's some font settings per OS :
https://github.com/pure-data/pure-data/blob/master/tcl/pd-gui.tcl#L284
What I see here is that it defaults to 'DejaVu Sans Mono' and always finds it. So if you try to load a general font for all of PD that the system can't find, then it just uses 'DejaVu Sans Mono' instead. So yeah, I believe Pd defaults to 'DejaVu Sans Mono' and finds it, but eve so, it seems rendering is not 100% - But that wasn't my main question, I just wanted to confirm this.
I tested on Linux and it couldn't find 'Times' or 'Helvetica' and it did default to 'DejaVu Sans Mono'. Now, what I'm asking is what happens when you choose 'Times' or 'Helvetica' for a GUI label. I know it doesn't find it and that I don't have it, but it loads pretty similar fonts that are not 'DejaVu Sans Mono'. So my main question is how can we learn what font is actually being loaded in these cases.
Moreover, when I try to load a non existing font in cyclone/comment, it does load some font that I have no idea which one it is, and it seems to be different for each platform - how can I find this out?