Part of the difficulty in identifying sources on this is that the concept of "ethnic dress" is strongly tied to nineteenth century/modern folk dress - regionalism played quite a lot into fashionable dress, historically. And fashion history as a field is unfortunately dominated by the study of English and French elite clothing. But some books to consider:

Dress in Eighteenth-century Europe, 1715-1789, by Aileen Ribeiro: the focus is more on French fashion, but other areas are dealt with. By the end of the century, French elite fashion had become an international standard, so the comparisons are important.

A Cultural History of Dress and Fashion in the Age of Enlightenment, edited by Peter McNeil: This contains a chapter by Dagmar Freist, which contains research on northern German middle-class dress (although I should note that it doesn't focus on it).

Primary sources, but they should be very helpful to you - these can be found in the Bunka Gakuen Digital Library:

Recueil de la diversité des habits, qui sont de présent en usaige tant es pays d'Europe, Asie, Affrique & illes sauvages, le tout fait après le naturel, 1562

Habitus variarum orbis gentium = Habitz de nations estrầges = Trachten mancherley Völker des Erdskreysz, 1581

Omnium pene Europae, Asiae, Aphricae atque Amerecae gentium habitus = Habits de diverses nations de l'Europe, Asie, Afrique et Ameriq[u]e = Trachtenbuch der furnembsten Nationen und Volcker Kleydungen beyde Manns und Weybs Personen in Europa, Asia, Africa und America, ca. 1610

Livre curieux : contenant la naifue representation des habits des femmes des diuerses parties du monde comme elles l'habillent à present, 1662

Costumes civils actuels de tous les peuples connus, dessinés d'après nature, gravés et colories, accompagnés d'une notice historique sur leurs costumes, mœurs, religions, &c. &c, 1788