I think that is questionable.
The use of the aramaic as a lingua franca and a prestige language in a large part of west Asia is well known but it's a language, not a full culture (this should be considered in the culture system, btw).
Aramaic - Wikipedia
en.wikipedia.org
The romans didn't encourage the spread of hellenic culture in the eastern Mediterranian, they tried to spread their own latin culture (with little success) and, after the split of the empire in two halves, the Eastern Roman Empire (aka Byzantine Empire) adopted hellenic as primary culture (Basileía Rhōmaíōn).
Byzantine Empire - Wikipedia
en.wikipedia.org
I agree that Aramaic was a language and not a culture that was shared by all speakers of Aramaic. But I think this is pretty much the same with Greece and Latin and Roman culture. Just as you can speak Aramaic and that language does not per necessity mark you for a Aramaic culture, so you can reasonably speek Greek and still be Roman as opposed to a Hellene in culture.
Is it more complex than this? Yes, but since the game does include language as a separate part of a character or POPs identity so it must be rolled into the culture tag. As such culture represents an lingo-ethno-cultural identity, and even less so localized forms of culture such as Thraco-Roman, Gallo-Roman etc. cultures. And thus we must accept some simplifications in this regard.
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