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Mine isn't so much of a historical nitpick, more of stylistical. 
IMO the French spelling of Karl's name sorta stand out from the rest of this Germanesque fantasy setting.  You know: Hrotsvitha, Hjortvad  and then ... Charlemagne for a dude even was a Germanic king.  Maybe even better call him "Karl the Great", it will be understandable for a general public and will be able to denote as if chars speaking their native languages and it is translated to English (or whatever localization are chosen) for our convenience.

In short I thought that French spelling of his name not fit the setting. 

Snouldn't "Charlemagne" instead of french prounouncation called german or latin way, "Karl der Grosse" or "Karolus Magnus"?

The game takes place in Skandinavia, there was no french speakers here,  and king Karl himelf came from german and latin speaking elite. It sorta breaks the immersion, that person wasn't called modern anglo-french way in this region especially when he was alive.