Users may want to start the week on a Sunday, Saturday, or Monday without changing their locale's date formatting.
CCBUG: 390330
If accepted, I'll be adding something a cleaned up version of the following patch to DigitalClock, Calendar, ... and the rest I guess.
https://github.com/Zren/plasma-applet-eventcalendar/commit/31c584900f318c8ae148ae9fbcc0ed58eccc5d9d