@jackie_w, shadow fonts (sideloaded fonts that are the same as built-in ones) are not picked up on reboot without post #2. I overrode the
Avenir Next using the one from the Nook package (while Kobo has updated Amasis & Malabar they left Avenir out, go figure). It is clearly overriding as I can now see Cyrillic glyphs in the book and there's a single Avenir Next in the font selection menu, but the home screen defaults to something else on boot. So clearly my original excitement was just stemming from my ignorance about built-in Amasis supporting Cyrillic
Let me know if you want me to test anything else, cause I'm out of ideas
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