I think usually you can say: K is Greek and C is Latin. But in the case of Carl/Karl this does not really apply, because
Karl (this is the
German form) obviously is a genuine Germanic name (see my post "Maybe
Karl is not a Man" ab few days ago). But in the Middle Ages everybody spelt his words the way he wanted to, so there was a lot of to and fro between some letters and C and K were some of them. I would say the Latin influence on the
German language was stronger then (let's say around 700 A.D.), but I don't really know much about this.
Andy ;—)