Hi Kjetil_r. Maybe I misunderstood something. DDO: prins has sense 1.b "(titel for) mandligt medlem af visse europæiske fyrstehuse". I took that for a principality, but I might be wrong.
Using prins in the "mandligt medlem af et europæisk fyrstehus" sense is seems correct, but it shouldn't be used to refer to the head of the principality.
Take Albert of Monaco as an example: As long as Rainier was alive, Albert should be referred to as prins Albert. When his father died and he became ruler, the correct title is fyrst Albert (even though many newspapers would get it wrong and still use "prins").
I just corrected "prins" here, as a "male member of an European princely family" definition better reflects the Danish "mandligt medlem af visse europæiske fyrstehuse" meaning.
In Danish both "Fyrst" and "Prins" is a correct title for the ruler of Monaco, but "Fyrst" is exclusive to the ruler not other male members of the family.
In my view, the sense "son or male-line grandson of a reigning monarch" covers the male members other than the ruler, so I'm going to revert your change.
Sorry if I mixed up the templates (or applied them wrong), I'm not used to the template naming conventions and usage at the English Wikisource.
I'm not going to spend more time arguing about what is correct in Danish, but I nevertheless still strongly suspect that the "Prins Albert" form – like it is in Norwegian – indeed is a mistranslation. It is probably like "w:da:prins af Wales" – a term properly translated as "fyrste af Wales" – where the translation error has gained common usage. We should of course not hide that "prins" now is used by some in the new "male ruler or head of a principality" sense, but we should make it clear that "fyrste" is the form traditionally preferred in the "male ruler or head of a principality" sense. I cannot remember seeing "prins" used in that sense when reading scholarly literature in Danish (for example in Politikens Forlag's many good books about history or politics, which I have often read at my local library).