Josef comes from the Latin name Ioseph and Greek Ιωσηφ (Ioseph), both derived from the Hebrew name יוֹסֵף (Yosef), meaning "he will add" (Behind the Name).
Wronski is a nickname derived from the Polish word wrona ("crow") (Behind the Name).
Lexicon list of Seekers
From the Web
Writing by J.K. Rowling on Pottermore: History of the Quidditch World Cup
Pottermore feature: Quidditch collection
Harry Potter Wiki: Josef Wronski