A cipher used by exiled royal princes in the years immediately after the French Revolution in 1789 is printed in Lindenfels (1819), the first book on cryptography in Danish, as I was taught by Franksen (1985), p.26. Lindenfels, a military officer embittered with the French right after the Napoleonic Wars, obtained it from "a noble benefactor", who inherited it from his father, who was one of the correspondents of the princes and was even named in the nomenclature, though not in the correct spelling because of "the bad habit of the French more or less to maltreat most non-French proper names". The same benefactor provided Lindenfels with Danish diplomatic ciphers (see another article). (I could not figure out which name in the nomenclature is referred to. Lovendal, which should be Løvendal (d.1808) (Wikipedia)?)
The cipher is a simple Caesar cipher, in which each letter of the alphabet is replaced by the fifth letter after it, but provides a slight complication by numerical homophones for the vowels. The nomenclature represents names by two-letter codes.
Since it was used while the exiled princes were in Coblenz (Wikipedia, Wikipedia) and later in other towns, Lindenfels calls it "the Coblenz cipher."
The example given is:
Ole Immanuel Franksen (1985), Mr. Babbage's Secret
J. B. Lindenfels (1819), Den hemmelige Skriwekonst eller: Chiffrer-og Dechiffrerkonsten [Art of Secret Writing] (Google)