Nearly all of the principal actors and actresses were using their natural accents (be they American, Russian, Czech, Italian, et cetera) with a few notable exceptions.
Mark Ryder (Cesare Borgia) and
Diarmuid Noyes (Alessandro Farnese) are Irish but used English accents on the show. Even
Stanley Weber (Juan Borgia) moderates his French accent, though he doesn't sound as English as his on-screen brother. This is because the series was intended for dubbing into non-English European languages (French, German, et cetera).
