Hello everyone,
I followed THIS example in order to set first day of week as Monday.
It seems to work fine as it is on this example it is set to “Montag”.
Problem that I faced and that I could re-produce on your localization example is when working with recurring events:

As shown on this screenshot I have created Weekly recurring event for every day. Pattern is also set to repeat every second time (week).
And this is result of that action:

As you can see event is not added for Sunday (Sonntag) for first week when events should occur every day.
If we inspect next week when we shouldn’t have any events since by pattern events should occur every second week, but we got this instead:

This problem only occurs if we add recurring events and set first day of week as Monday.
Is there any solution for this problem ?