These 3 things will make me start playing this...
Great!
And, wasn't it Vojvoda ( like it is now and was always in the south-Slavic languages, Croatian also has Knez for THAT title <all have Knez but more as a military leader than a duke like Vojvoda / Voivode is in other languages> )
Voivode could be kept and would be accurate and actually readable with quality by non-Slavic peoples, yet voivodE is a plural noun, voivodA isn't... 
So ye, another fix and it'll be fine
Yes, Vojvoda is a correct term.
I have named them
Voivode because that's an anglicesed form of
Vojvoda.
I have chosen the English term because all titles in our mod are translated to English (King, Sire, Lord, Bishop, etc.),
EXCEPT the titles that don't really have an English equivalent (Podesta, Ban, etc.)
Now, the fact is that Vojvoda doesn't really have a true English equivalent/translation (except the anglicised form Voivode).
So I would have put them as Vojvoda, but, other than Serbia and Bosnia, Vojvodas will be present also in Bulgaria, Poland and maybe in Russian states (in the future releases of the mod).
Bulgarian term is Voyvoda, Polish is Wojewoda and Russian is Voevoda.
So, I have suggested that all those states share a title - the English word Voivode.
As for
Knez, the English term is
Prince. Many nations in the mod have that title.
