[Solved] DateTimePicker not being translated

I have installed the suggested package (Telerik.Windows.Controls.for.Wpf.Xaml.es), and I have set the culture with the following code:

            var newCulture = new CultureInfo("es-ES");
            var dateInfo = new DateTimeFormatInfo
            {
                ShortDatePattern = DateTimeFormatter.ShortDateFormat,
                ShortTimePattern = DateTimeFormatter.HourFormat
            };
            newCulture.DateTimeFormat = dateInfo;
            CultureInfo.DefaultThreadCurrentCulture = newCulture;
            CultureInfo.DefaultThreadCurrentUICulture = newCulture;
            Thread.CurrentThread.CurrentCulture = newCulture;
            Thread.CurrentThread.CurrentUICulture = newCulture;

And the result is the same: the filter has been translated but the calendar is still in english:

Hello, Román,

It seems that when you create a new DateTimeFormatInfo and assign it to newCulture.DateTimeFormat, the new DateTimeFormatInfo is constructed with invariant culture defaults — not from "es-ES". This effectively overwrites the Spanish date/time formatting (day names, month names, calendar, separators, etc.) with English/invariant values.

I would recommend you to set ShortDatePattern and ShortTimePattern as follows to take effect. Use the following code snippet:

public MainWindow()
{
    var newCulture = (CultureInfo)new CultureInfo("es-ES");
    newCulture.DateTimeFormat.ShortDatePattern = "dd/MM/yyyy";
    newCulture.DateTimeFormat.ShortTimePattern = "HH:mm";

    Thread.CurrentThread.CurrentCulture = newCulture;
    Thread.CurrentThread.CurrentUICulture = newCulture;

I also attached my sample project for reference. You can give it a try and see how it works. Everything is translated into Spanish automatically.

I hope this helps. Let me know if you have other questions.