Most of the UI fonts are configurable via resources, but it seems there are some elements where DejaVu is hardcoded and not exposed by an option. For example, the "rulers" in the glyph editor do not seem affected by the config.

If a user wants to change the default UI font, doing so via resources is insufficient. This makes for an inconsistent UI, and makes it necessary to override DejaVu in fontconfig in order to get consistent UI fonts in fontforge.

One way to change this is to re-order the desired fonts. These appear to be in a few places:

fontforge/pixmaps/tango/resources-georgd
fontforge/pixmaps/tango/resources
fontforge/fontforgeui.h
gdraw/ggadgetP.h

I propose changing these according to:

- dejavu sans,helvetica,caliban,sans,clearlyu,unifont
+ sans,dejavu sans,helvetica,caliban,clearlyu,unifont

and doing similar for serif and monospace.

I imagine this might be considered undesirable because it makes changing one's default sans-serif, serif, or monospace in fontconfig the easy way to change the fontforge UI fonts. Otherwise, it's an easy change that should affect the entire UI.

Here are a couple examples with all the fonts being replaced:
Fira Sans

Helvetica