Pertaining to Redride's OG:
-French as we know it is the Francien in the game - Parisian French. France also already exists, so a more suitable medium would be events that gradually change the culture.
-Czech: Again, there isn't really a country to form here, so I wouldn't really know how to implement it.
-Spanish is just another name for Castilian, and if you don't believe me you may look it up.
-Arabic would be interesting, I won't take it off the table.
-Yugoslav is interesting but I'm not sure it's wholly accurate. I'm also not real interested in adding a Yugoslavia tag.
-Yemeni is hardly worth splitting up like that
-Indian may be feasible, perhaps a little overpowered lol.
-I don't know how I would implement a Han culture
-Japanese has merit
-Occitan is already a culture in the game? I'm not sure what you meant by this.

Pertaining to Dr.Frizo SenPaiO:
-Magyarisation did not occur within the game's time period, and then Slovak and Transylvanian are already a part of the group Hungarian is in. I disagree with that but it's for gameplay reasons, which also brings me to the second point:
-I am not going to be editing existing cultures, only adding so I don't have to worry about any more compatibility issues or issues with updating the mod.

How about an Arab national culture, to represent a Pan-Arab union
(nvm you already considered it; in that case I support this idea)