Microsoft project currently supports default calenders (Gregorian, Hijri, ...). You can switch calendars from: File > option > display > calender type
When the calendar changes, all months and weekday names change according to the selected calendar throughout Microsoft project.
The question is: How to develop new Calenders to be used in Microsoft project?
I expect the road map of developing new Calenders (as 3rdparty plugins) to be used in Microsoft project.