Font fallback mechanisms have more counterintuitive quirks than one might think. For example: I needed a few pictograms to mark land and sea access for some UI element. The obvious solution — using Unicode mountain and anchor glyphs — led to an interesting adventure. The font I use (DIN1451 for Latin), of course, lacked the needed glyphs. Not a problem, you might say: just add them to the font file and be done with it. Turns out it’s not that straightforward. While the mountain “letter” (U+26F0) worked fine, the font engine stubbornly refused to use my anchor (U+2693) glyph. The eventual solution was to move both glyphs from their standard codepoints (26F0 and 2693) to the so-called Private Use Area (U+Exxx). After that, the font engine started using whatever the font actually has.

Still not sure whether this is a Godot quirk, a system font engine quirk, or a Unicode nuance.