I am from Holland. In Dutch, we have the word "Volk" to describe the masses of people formed by a group with genetic, cultural, and ideological bonds and similarities. So in Dutch "Volk" is the proper original noun for "ethnic group" just as in English the proper original noun is "folk" (and not "people", since "people" is latinate).
Now in Holland we use the words "Volken" or "Volkeren" to describe the plural of the word "Volk", so they describe a set of several different ethnic groups. We use the word "Volks" when we use it as an adjective, both in the singular and plural forms. As a singular term, it would translate into English as "folkish".
However I am searching for the translation of the adjective used as a plural. In English, a plural is mostly created with an "s" after the singular, so that would make "folks". However, where "folks" in English can be used to define just a group of people, "Volken" or "Volkeren" as nouns in Dutch would never mean just a group of people, just as the Dutch adjective "Volks" used in the plural never would. It would always mean a set of different ethnic groups.
So now I am searching for one single word that, as in Dutch, describes "a set of different ethnic groups" like the word "Volks" without running the risk that folks think I am just talking about "a set of people". There is a large difference between the definitions of "a set of different ethnic groups" and "a set of people", and I need to make a headline in which I have only room for one word to communicate the correct meaning.
I should be able to use it in the translation of the Dutch sentence
"En het vrije volks verbond leeft voort...."
which in English would be
"And the free XXXX federation lives on...."
where XXXX is the word I am searching for.