Use internal category name

internal/pretix/order_placed.go

@@ -222,9 +222,7 @@ func (s Server) fetchCategory(organizer, event string, item uint) string {
 
 	decoder = json.NewDecoder(resp.Body)
 	itemCategory := struct{
-		Name		struct{
-			German	string	`json:"de-informal"`
-		}
+		InternalName	string	`json:"internal_name"`
 	}{}
 
 	err = decoder.Decode(&itemCategory)
@@ -232,7 +230,7 @@ func (s Server) fetchCategory(organizer, event string, item uint) string {
 		return ""
 	}
 
-	return itemCategory.Name.German
+	return itemCategory.InternalName
 }
 
 func parsePrice(price string) (euros uint64, cents uint64, err error) {