'Declaration Public Property FirstDayOfWeek As Nullable(Of DayOfWeek)
public Nullable<DayOfWeek> FirstDayOfWeek {get; set;}
By default the FirstDayOfWeek is set to null. When set to null, the System.Globalization.DateTimeFormatInfo.FirstDayOfWeek from the control's System.Windows.FrameworkElement.Language will be used.
Target Platforms: Windows 10, Windows 8.1, Windows 8, Windows 7, Windows Server 2012, Windows Vista SP1 or later, Windows XP SP3, Windows Server 2008 (Server Core not supported), Windows Server 2008 R2 (Server Core supported with SP1 or later), Windows Server 2003 SP2