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Unknown things are always fun, not to mention switching out demon abilities, but make sure they have something identifiably different. I have used demons and devils from many settings myself, and changed known ones to something different, but also made a cosmetic change. Players can tend to memorise stat blocks, so i change the stat blocks.

I think that is mainly a question for your GM - "Are you okay with importing demons from Rifts: Russia and Rifts: China to our Palladium Fantasy campaign?" It will at the very least involve some work for them converting, and may not fit well in the campaign (for reasons they may or may not even be able to tell you about!), so it is always best to check with them first!

If they are okay with it, then you would both have to work out how your character could even find out they exist, let alone learn enough to summon one. How would they know about creatures from Rifts Earth? It then becomes up the the GM's generosity to decide wither you coincidentally find a book on Russian demons in your local library, or whether they insist you need to spend weeks or months seeking out obscure demon information in order to achieve your goal; talking to secretive summoners rumoured to have experimented with rare demon types, searching for a famous interdimensional traveller who claims to have visited the Eleven Kingdoms of Hell, and of course, long, long hours of study in the Library of Beltherad. Some of these might be incompatible with the general course of the adventure or the goals of the player group as a whole.

And would it require a while new circle of summoning to be learned/invented? If there is a separate circle for demons and deevils, perhaps there needs to be separate ones for Russian, Chinese, Japanese and other "families"?

It is good to shake things up with new stuff after a while. Have you looked at the Minions of Darkness in Land of the Damned book 1? They are described as demons, and it would probably be easier for your character for learn about and summon one of those. Or "the Fallen" and other additional demons and Deevils found in the Rifts dimension books of Dyval and Hades?

It's up to the GM, really. Swapping things in from MDC settings can be dicey (lots of room to make a mistake, IMO), but I'd allow it... though the standard summoning circles may not work, and you'll need to make some modifications.