Wait, are we talking about nationalities, languages, or cultures? Or are we talking how to relate those WITH the Discovery universe?
It's not that hard to go a little out of the standard cannon and add an little exotic flavor to a house or so.
There was a sort of squadron/battlegroup in bretonian that claimed that it was composed of descendants of Portuguese and lusophone members who were "aligned" with the British navy in the Sol war.
There is/was that native american group in the Taus, (aligned with the french/gauls?).
I made a secondary KNF pilot with a korean surname, for some variation. (although he doesn't diverge from other kusarians more than that).
There was a for a period of time a group of chinese named GMG players active, even though the Coalition claims that they retain all the humans with Chinese ancestry in their ranks.
Lots of kusarians in LIberty and Gallia ranks. Zoners of every kind. The list goes on.
Not all Libertonians are yankees, not all Bretonians need to be from either England or Ireland (where are the welsh?)
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P.S. from the wiki on dead language
"In linguistics, language death (also language extinction, linguistic extinction or linguicide,[1] and rarely also glottophagy[2]) is a process that affects speech communities where the level of linguistic competence that speakers possess of a given language variety is decreased, eventually resulting in no native or fluent speakers of the variety. Language death may affect any language idiom, including dialects and languages.
Language death should not be confused with language attrition (also called language loss), which describes the loss of proficiency in a language at the individual level.[3]"
Dead langages are those that have no native speakers, or speakers who have that language as it's mother tongue. Sure there are a lot of Latin learners, but none of them are raised and educated with Latin as their mother tongue.