In App.xaml.cs, add;
CultureInfo ci = new
CultureInfo(Thread.CurrentThread.CurrentCulture.Name);
ci.DateTimeFormat.ShortDatePattern = "dd-MM-yyyy";
Thread.CurrentThread.CurrentCulture = ci;
It will be like this;
public App()
{
this.Startup += this.Application_Startup;
this.Exit += this.Application_Exit;
this.UnhandledException += this.Application_UnhandledException;
CultureInfo ci = new
CultureInfo(Thread.CurrentThread.CurrentCulture.Name);
ci.DateTimeFormat.ShortDatePattern
= "dd-MM-yyyy";
Thread.CurrentThread.CurrentCulture
= ci;
InitializeComponent();
}