He just wants to be Valerian (GoT).
Also, there isn't really any racism in the game. If any would be present , some aversion between some cultures and lords (with 'that which is foreign'), and yet there would also be some respect. Some freely expressed, and others only grudgingly for what the culture brings in terms of effectiveness with certain troop types, etc.
I admit myself that I try to keep foreign troops in garrisons as minimum as possible, as otherwise the uniqueness of each in battle can be lessened (and for when the colors of empire factions are way too close in hue to others, while I prefer to play with banners off).
Despite that, I usually keep a large number of Kuzait horsemen and archers, Vlandian (Sergeants, crossbow, voulgier, bannerknights), and view Imperial troops as being 'lesser' than them (cavalry culture and Foot-knights are better than the average troops of Empire), even though my culture is empire.
Ah, reminds me of Warband.... I always loved fighting against the Khergit... each battle you try and get your troops in a good placement right before the unstoppable wave of horse archers and lancers charge.... really fun stuff. Same thing with the 'Jatu' in the Prophesy of Pendor mod for Warband (really great if you haven't already tried it).
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But getting back to original post, to have 'unique reactions and behaviors' depending on character background might not be best use of time/effort when this is such a small detail, and many other features far more deserving in all things are still in progress.
If you really want to have some racism you can just make the voices or dialogue yourself 'get outta my bar you sand-carpet, I just swept it!'