Actually
Visnja is not the alternate spelling of
Vesna. It is a different name.
Visnja means sour cherry ( Prunus cerasus is the latin name of the plant) in croatian/serbian. Fruits are smaller and darker than in the ordinary sweet cherry and they are not sweet. A famus sort of sour cherry is grown near the dalmatian town of Makarska - it is called Amarena. They make a delicious juice from them (the kind of juice you dillute with water).