Complex sentence: But the most significant is the event held from 26th to May 31st by the name "Pastirski dani" (loosely translated: "Shepherd days") with regard to exhibit various sorts of sheep.
Split into simpler sentences: But the most significant is the event held from 26. May by the name "Pastirski dani" (loosely translated: "Shepherd days") with regard to exhibit various sorts of sheep.