There are several Russian/CIS 737 operators, which most writing here are doubtless aware of.
Belavia have a couple of 737s. Russian is the technical language in Belarus and they would have no use for anyone who was not fluent in the language. I would guess that Belarus and Russian nationals fill all their needs so that is as far as they need to go. There is a considerable continuing affinity between Belarus and Russia, which cannot be said for most of the other CIS countries nowadays.