I wouldn’t recommend swapping out any of the Butterfly keycaps since the 2015 MacBook and the 2016 MacBook Pro’s to the 2019 the keyboards are just too fragile!
The newer Magic keyboard which goes back to a newer scissor design is just too new to know if the keycaps are even serviceable and I wouldn’t recommend swapping out the full uppercase just to changeout the keyboard as that’s a $1,000 USD expense! The iFixit team did do an experiment swapping out on of the Bluetooth Magic keyboard keycaps with there 16” system as you can see here MacBook Pro 16" 2019 Teardown Jump down to Step 5, so its possible! I still would not do this as one keycap is still a long way of a full keyboard.
The best way here is just get a keyboard stickers or full cover which has the markings for Russian.
Russian Cyrillic Stickers
Russian Cyrillic Keyboard Cover You’ll need to talk to them for the 16” model as its not listed.