Sure. I couldn't find it, but I'm basing it on an old thread where (I think) Johan said that's what culture and religion represent - the culture of the people who matter in the local area basically. You're right, ruling people would be multilingual - Joseph II of Austria would have time set aside where any subject could come and speak to hit, and they would converse in their native language; Philip II and Mary Tudor's spoke to each other in Latin and French. Among noble classes, certainly earlier in this period there was a comradeship - certainly compared with comradeship with peasant classes. Nationalism is a middle class invention after all. The Vic II pop system is fantastic because that is a game about nationalism. EUIV is a game about lots of things, but primarily the state. Nationalism doesn't feature in EU4 until right at the end.
I think chasing it back would be adverse. Slovak and Hungarian are in the same group because of the historical close links between the two ruling classes., as an example.
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