It seems mostly sung by Czech choirs (listed as "Voro Ivaničky", and most of their repertoire lists indicate simply "folk", even when they denote the nationality of other folk songs. However, judging by my knowledge of both Czech and Russian, while Ivanička and Maruška are typical diminutives of the names Ivana and Maria, neither "voro" nor "jestofar" translate. One Czech choir clearly categorizes it as a foreign song, and elsewhere it is attributed as Estonian, Bulgarian or Ukrainian, though online translators do not recognize voro or jestofar in these languages either. The song often bears a translated title of "Whatever it may be" (or are they referring to the nationality of the song?) Having the full lyrics would help.