You know speaking of cultivation systems I imagine there are some old roman (pre christian) and Greek cults hidden around.
It seems like you need a whole living culture for a cultivation system in this world, so an isolated cult probably doesn't have the mojo unless they're tapping into something the majority of the populace would acknowledge as real (ie: you can probably do a Satanic cult in Christian lands since they believe in that...a pagan cult to a God no longer worshiped outside those lands would be much harder).
Do the Lithuanians/Baltic people have something based on Romuva?
Probably, though we lack confirmation.
Did you make something for the Sunni/Muslims?
We've had it confirmed there's an Islamic Cultivation System, but absolutely no details on what it's like.
I believe the 'confirmed' list is Norse, Finnish, Feudal/Christian, Byzantine/Imperial, Islamic, Chinese, Japanese, and Hindu. Sami was also sorta confirmed when they got brought up, I think. We've theorized several others (and it's been stated that those aren't the only ones), but those are the confirmed ones, I think. Very little has been confirmed
about any of them but Norse, Finnish, Feudal/Christian, and Byzantine/Imperial, which have all had various details put forth in varying amounts.
We know the Finnish have something different so most of places east of them should be that or similar.
Do the Slavs have something different or similar.
... Sorry ideal thoughts and curiosities.
We haven't heard anything about the Slavs, but some sort of separate cultivation seems possible, yeah.