Translation:During the winter they live in small bilingual groups.
For example: https://en.wikipedia.org/wiki/Seasonal_migration_in_Niger Seasonal migration in humans exists and especially if we talking about history we could imagine this resulted in small bilingual groupings of people! :)
English used to have this too and there are still vestiges of it today - think of the game "never have I ever." It's also why a comma appears when time/location is put at the front of the sentence in English - "on the roof, a cat sat" and "on the roof sat a cat" are both grammatically correct, although the latter is stylistic and usually only found in things like literature and poetry these days. But the comma in the first one is there because you need a new clause for SVO order.