How to localize the GridDateTimeColumn button text in WPF DataGrid (SfDataGrid)?
The DateTimeEdit control as an edit element for GridDateTimeColumn in WPF DataGrid (SfDataGrid). The DateTimeEdit control referred by Syncfusion.Shared.Wpf assembly. You can localize the GridDateTimeColumn button text by adding the resource file as Syncfusion.Shared.Wpf.<culture name>.resx.
public MainWindow()
{
System.Threading.Thread.CurrentThread.CurrentUICulture = new System.Globalization.CultureInfo("de");
InitializeComponent();
}

The following screenshot shows the localized GridDateTimeColumn button text,