My system language is Arabic, if I add
System.Threading.Thread.CurrentThread.CurrentCulture = new CultureInfo("en-US");
System.Threading.Thread.CurrentThread.CurrentUICulture = new CultureInfo("en-US");
dtpBTStartDate.Format = DateTimePickerFormat.Custom;
dtpBTStartDate.CustomFormat = Application.CurrentCulture.DateTimeFormat.LongDatePattern;
Answer: If the OS UI language is Arabic I believe all
MonthCalendar controls will be shown with Arabic UI, because those controls are just a wrapper around
Note: As an alternative you can use 3rd party libraries. The free open source FarsiLibrary is an option. While the library is called FarsiLibrary but its DateTimePicker and MonthView controls supports Jalali (Shamsi/Persian), Hijri (Qamari) and Gregorian calendars. Here is the link for codeproject article, page of the library in the author's site and the nuget package.