My question is about using a Ph.D. title/grade from an EU University in Germany. Germany recognizes (properly obtained) Ph.D.s from other EU countries. People with an EU Ph.D. are allowed to use the abbreviation "Dr." in front of their names without mentioning the country of origin (which is AFAIK required for some other countries) or using the original version. However, reading this information letter from the Bavarian State Ministry of Sciences, Research and the Arts, section 1.3.2. (German), you are not allowed to use both together.
I'm confused about this and its exact scope. Does this mean a Ph.D. holder can't call him-/herself "Dr. Firstname Lastname" on a business card and then list "Ph.D." together with the other titles like "M.Eng., Dipl.Ing." on a second line? Using "Firstname Lastname, Ph.D." in Germany would not have the same effect then the first form. Not mentioning the Ph.D. at all however would keep many people wondering what kind of doctor grade you have. Maybe it only means not to use "Dr. Firstname Lastname, Ph.D.", but the business card example is very close to that.
Also, can "Ph.D." be used in one occasion and then "Dr." in a different one, or do you have to stick with one? Would it be ok to use "Dr." on your German business card and "Ph.D." on your English one? Even if both are on opposite sides of the same card?
If I am not mistaken, you may decorate your name with "Dr. Dr." if you have two PhD degrees. Writing "Dr. Firstname Lastname, PhD" would probably also indicate two degrees, e.g. one from Germany and one from the UK.
PS: The information letter is no longer available, so I have not read that.