Comment # 1 on bug 1053947 from Wolfgang Bauer

Works fine here, with both the latest 17.08.0 and 17.04.2 as shipped in Leap
42.3.

Did you actually configure the desired holiday region in KOrganizer's settings?
(Settings->Configure KOrganizer->Time and Date)
The default is "None", which will of course *not* display any holidays.