how so ?
the romans managed to romanize large parts of the world, the russians managed to assimilate large parts of Non russian people. the slavs slavized the pre slavic people of the Balkan etc.
So, having migrating tribes scattering about is not equivalent to the Roman Empire's sustained and powerful presence in the West (in the East, the Romanization was relatively superficial), not sure how much the Russians Russified nonRussians, and the Slavs were only partially successful in the Balkans.
You don't have anything providing a force for the natives to either change their ways or be forced out over the entirety of this area.
To pick an example of a successful group, France takes its name from the Franks, but its language more from the Romance direction than the Germanic direction of the Frankish language.