Short answer, KiCad can only use it’s builtin font.
In theory, one can write some Python code to get system fonts, render onto in-memory bitmap, then convert the bitmap to polylines which could be inserted into the PCB. There are scripts to insert bar codes for example. For curiosity, I did some experimenting with system fonts along those lines. It’s a somewhat convoluted route, and the results may not be that great. I think if I had a real need for it, I would look at converting SVG or something directly to Gerber, or as direct as the Gerber format allows.