As far as I know you have to be a Russian national (resident) to be able to be part of the flight crew.
So that is part of the reason for flight crew shortage.
I wasn't able to figure out if this law has been approved by the Russian government, but things shall change (improve?) a bit soon:
Russian Transport Chief Asks Govt to Speed Up Foreign-Pilot Law | Russia | RIA Novosti
Flying within Russia is a great experience and I encourage fellow pilots to apply there once allowed to do so, besides the fact that salaries are competitive.