Margrave and Markgraf are the same thing, You can always search it up if you're not convinced.
I see. From a (jp) speaker, I don't ever see markgraf used over margrave. But from a translation standpoint, it's just a little strange to see an origin spelling instead of the modern global, given that the other names or titles used the latter.
It's either a translation error or they deliberately used the German term instead of the English margrave or the French marquis, because of the settings or something like that. I'm good with either of them.
I checked out the raws just in-case but, the translation is a little off here (which is why it reads so strangely) and there and it could use proof-reading. Also I'm pretty sure it's meant to be Margrave and not Markgraf. Margrave is a title given to a prince.