AFAIK, Georgia is a Microsoft font that won't be available on the Nook unless B&N has licensed it, and since you specified serif
as the fallback font, your book will be displayed with the default Nook serif font, which most likely looks like Times New Roman.
In order to avoid this problem, you'll need to embed a free font similar to Georgia. Popular choices are Charis SIL
and DejaVu LGC
, which both support the accented letters that you need for displaying Dvořák
You can embed them manually
or have Calibre do it for you
by doing an epub to epub conversion.