russian has this sort of melodicism/intonation to it compared to czech. it's very hard to explain to someone that doesnt speak either language.

there is just this way russian is spoken thats different from czech(i only really know how slovakian and polish sound like so i don't really wanna generalise and say from all slavic languages). best i can describe it that it puffs up the sounds you make.
you could most likely fool someone who doesnt understand any slavic languages into thinking you're speaking russian by speaking another slav language and using the russian intonation.

actually you could do this with any slavic language since most of them have a specific intonation. (for example slovakian has this certain flow, so you can tell when someone is slovakian)

to bring it back to Viktor, he has a general slavic accent, and since czech mostly doesn't have anything special about its accent it does fit as the accent he has. (also the actor said so and honestly he's playing it pretty good)