There is no option to set monday as the first day of the week. 

It is true that the americans use sunday, but literally the rest of the world doesn't.

The problem sounds quite like a one-line code adding a checkbox, but I read up some explanations and the program seems to pull the locale, and that's what you get. 

Can't you make some kind of hardcoded variable that supercedes the locale, and uses another one? Then again, how hard is it to call the first column Mon, and the last Sun, and shift the numbers by one? 

It's quite aggravating that such a fundamental feature is not included in a default xfce program. It's like shipping Windows, but only the notepad is in chinese for some reason.

Please finally fix, and realize just how many people you are dismissing with this. Hell, it's the ISO standard that the week starts on a monday!