Finland, Estonia and Hungary were all conquered by Mongolian and Turkish people in the early Middle Ages under conditions which brought about a linguistic change.
The Saami are a remnant (80,000+ people) of what may have been Europe's first population of modern humans. After the Black Plague which killed 90% of the Norse people in Norway, the Coastal Saami were enticed to take up Norse farms (presumably so taxes could be paid). 10% or less of the Saami suffered from the Plague although they live in an area where the dominant lifeform is the rat (and other rodents, e.g. lemmings). Their language is quite ancient ~ maybe more than we realize.