Oh, while the word 'Nationalism' may not have been heard yet, all the elements of that term were in play and born in the 1700s. Just a few examples;
"Every nation has its center of happiness within itself, as every ball has its center of gravity!”
"The universal dress of philosophy and philanthropy can conceal repression, violations of the true personal, human,
local, civil, and national freedom”
Jean-Jacques Rousseau wrote rather caustically regarding Corsica in his Projet de constitution pour la Corse  (Constitutional Project for Corsica)
"La première règle que nous avons à suivre est le caractère national. Tout peuple a ou doit avoir un caractère national et s'il en manquait il faudrait commencer par le lui donner." (The first rule we have to follow is the national character. Every nation has or ought to have a national character, and if it is lacking, it should first be given to it.)
English 1788 edition of The New Royal Encyclopædia under the heading ‘Nation.’ [This basically copied from Diderot’s and D’Alembert’s Encyclopédie,, published in France between 1751 and 1772.
These views add up to a national taxonomy, not a matter of reputation, stereotype or appearance but essential traits of the people and nation in question. National character became seen as a social and political force forming the logical basis for any kind of reform. Thus, national character moved from unquestioned tradition to that of an empirically-established theory with immediate practical applications.