We know that Sainze was close with Andre from the German novels, and given his story (picked up on accident of a Combine recharge station) that might be enough. But, more likely it came to the fore in the kindraa formation process, or just before. In a unified Clan, all the Sainze learning Japanese would be odd, but if they were planning to go their own way, it would be a good way to forge an independent identity.
The Carols are reputed to have Kerensky blood, implying closeness, so I assumed that was the source of the Russian element, but I can't recall what (if any) the relationship of the original Carol was.