PhD final grade on CV
You need to keep the intended audience of that CV in mind. If you are just interested in a German audience (non Germans can read your CV if they can find it, but you just don't care), then you can add those grades. If you aim for an international audience you need to give them a metric by which to evaluate those notes. For example, in the Netherlands a PhD can only get two grades: a regular pass (about 95%) and a cum laude (about 5%). So if a Dutch person sees a CV with a cum laude for a PhD (s)he will be very impressed, which is not what that note means in Germany.