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.