Grammar problems about Latin royal titles and place names
Recently I am reading about the Latin titles of monarchs. As someone interested in Latin, I want to know about whether the royals in general use their Latin titles in a grammatically or orthographically correct way, like "Fidei Defensor" or "Fidei Defensatrix". And since "Scotland" is "Scotia" or "Caledonia", Is "Caledonii", "Scotorum", "Caledonorum" or "Scottorum" the correct form for "of Scots"? And is it grammatically permissible to use both toponymic and demonymic names in titles, like "Rex et Regina Francorum Scotorum Angliae et Hiberniae"?
As to the first question, whether they use Latin titles in a correct way, the answer will be, almost always, yes. These terms will have been recorded by monks and scribes who spoke fluent Latin. There might be the odd error but on the whole they will have got it right.
As to the question of mixture of toponymic and demonymic names, this is an interesting question. In practice, I think they were often less fussy about this than we have become in pinning names to things. In general, of course, there has been a drift towards toponymic titles, but the extent to which this was deliberate and marked at the time is questionable.
Take for instance Philip II of France, possibly the most famous "transitional" monarch, who started out as "King of the West Franks" and ended his reign as "King of France". This is remarked as defining a shift in the French monarchy from an elective peer-review system to early absolutism. Well, maybe. But it was also a necessary correction. The kingdom of the Franks had been sundered for 300 years by his reign and was clearly never being repaired. And he didn't just rule over Franks: in tribal terms, his kingdom included Goths, Flemings, Bretons, Gascons... A toponymic title was not only more convenient but arguably more accurate. And terms like "West Francia" had been in circulation for a while already. (Arguably, "of France" doesn't clear things up if we take it back to source: it's a romanisation of "Francia" but France-so-called never included Franconia)
See also the kings of Sweden who (much more recently) transitioned from the lengthy "King of the Swedes, the Goths and the Wends" to "King of Sweden". And some kingdoms appear to have been founded with toponymic titles even in that same period. The Spanish kingdoms, including Navarre, were, so far as I'm aware, always toponymic. It might be that demonymic names were a peculiarly Germanic styling.
In practice, medieval kings of Scotland were frequently styled "of Scots" or "of Scotland" interchangeably, and the same in England. I have however been trying to think of an example of someone combining the two at the same time. Generally they tend to use titles of the same type when listing, and it doesn't help that translations are inconsistent. For instance Cnut is generally referred to as a king of Denmark and of England, but his actual style seems to have been "King of the Danes, Irish and English, and the Island-dwellers" - and with no mention of Norwegians or Swedes who were doubtless rather more his subjects than the Irish were.
I suspect, but cannot be sure, that Frederick II of Germany is our most likely suspect. As Emperor, he was "king of the Romans" but also separately King of Sicily and of Jerusalem. While there might be a title "King of the Sicilians" (albeit I don't think there ever was) I am certain that there was never a title "King of the Jerusalemians". However I have not been able to conveniently find corroboration of what Frederick's Latin title actually was.
In any case, the later medieval and early modern German rulers are probably the best place to look for examples, because they were frequently kings both "of the Germans" and/or "of the Romans" and also of, say, Bohemia.