Here’s a very resourceful web address containing many papers on Slavic mythology in English.
“Studia mythologica Slavica is international scientific journal on the mythology, spiritual culture and tradition of Slavic and also other nations and people. […] The journal is dedicated to interdisciplinary studies, and one of the main aims of this journal is to present comparative research that defines and determines (i.e. establishes) Slavic culture in the context of the wider European and non-European world (cultures). The journal intends to throw light on the belief systems and religions of older Slavic, Eurasian, and other civilisations.”
complete description here