How to set the first day of the week in System tray calendar?
Using regedit, browse to HKCU\Control Panel\International, look for the iFirstDayOfWeek key and set the value to 0 for Monday, 1 for Tuesday, 2 for Wednesday, etc ...
On Windows 10:
Right-click on the Taskbar Clock area. Choose
Adjust date/time
It opens a dialog, with a
Formats
section, where there is a display-only summary of options, includingFirst day of week
. Click the linkChange date and time Formats
On the dialog that now appears, you can choose what one you want on the
First day of week
combobox.
I ran into this exact issue when getting issued a UK-regioned desktop.
You need to go to Control Panel -> Regional and Language Settings
and pick a region that starts the week on Sunday, like US.