I selected India, Germany, and Japan.
1. I've covered my opinion on
India in the past; while I'm not greatly pleased by the UU and UB, they're tolerable. What really needs a change is the UA. I'd favor:
Sacred Rivers: Cities adjacent to a river receive +10%

growth rate and +1

faith.
This would reflect India as a religious civilization, which it was, while also giving them a growth bonus to reflect the large population. Happiness can be dealt with in other ways (hey, maybe with that early faith bonus you can take
Sacred Waters - you're going to want to settle on those rivers anyway!).
2. I've also talked about
Germany in the past. Again, I'm content with the UUs (though I think the Landschnekt would be more appropriate as a Longswordsman replacement, as they also used Zweihanders besides the pikes). My favored alternate UAs:
Furor Teutonicus: Military buildings (Barracks, Armory, etc.) confer +1

production. Pay 25% less for land unit maintenance.
~or~
Furor Teutonicus: When at war with more than one foe, all land units receive a +15%

combat bonus. Pay 25% less for land unit maintenance.
The former would reflect Germany's famed production while encouraging the development of military training buildings. Great synergy with the already low cost Landschnekt. The latter would reflect Germany's well documented tenacity when dealing with wars on multiple fronts.
3. As for
Japan, Bushido and the Samurai are fine. The Zero is just bad. Very late game, not very iconic or culturally relevant, replaces a unit that is underutilized, and it barely improves the Fighter anyway. I'd rather have some sort of UB instead.