Question

I have a .NET 4.0 WPF application where the user can change the language (culture)
I simply let the user select a language, create a corresponding CultureInfo and set:

Thread.CurrentThread.CurrentCulture = cultureInfo;
Thread.CurrentThread.CurrentUICulture = cultureInfo;

In the C# code this works fine. However in the WPF controls the culture is still en-US. This means for example that dates will be shown in the US format instead of whatever is correct for the current culture.

Apparently, this is not a bug. According to MSDN and several blog posts and articles on StackOverflow the WPF language does not automatically follow the current culture. It is en-US until you do this:

FrameworkElement.LanguageProperty.OverrideMetadata(
    typeof(FrameworkElement),
    new FrameworkPropertyMetadata(
        XmlLanguage.GetLanguage(CultureInfo.CurrentUICulture.IetfLanguageTag)));

See for example StringFormat Localization issues in wpf.

I do not completely understand what is going on here. It seems the Language property on all frameworkelements is set to the current culture. Anyway, it works. I do this when the application starts up and now all controls works as expected, and e.g. dates is formatted according to the current culture.

But now the problem: According to MSDN FrameworkElement.LanguageProperty.OverrideMetadata can only be called once. And indeed, if I call it again (when the user changes the language) it will throw an exception. So I haven’t really solved my problem.

The question: How can I reliably update the culture in WPF more than once and at any time in my applications life cycle?

(I found this when researching: http://www.nbdtech.com/Blog/archive/2009/03/18/getting-a-wpf-application-to-pick-up-the-correct-regional.aspx
and it seems he has something working there. However, I can’t imagine how to do this in my application. It seems I would have to update the language in all open windows and controls and refresh all existing bindings etc.)

Answer 1

I never found a way to do exactly what I asked for in the question.
In my case I ended up solving it by having all my usercontrols inherit from a superclass that contained this:

/// <summary>
///   Contains shared logic for all XAML-based Views in the application. 
///   Views that extend this type will have localization built-in.
/// </summary>
public abstract class ViewUserControl : UserControl
{
    /// <summary>
    ///   Initializes a new instance of the ViewUserControl class.
    /// </summary>
    protected ViewUserControl()
    {
        // This is very important! We make sure that all views that inherit 
        // from this type will have localization built-in. 
        // Notice that the following line must run before InitializeComponent() on 
        // the view. Since the supertype's constructor is executed before the type's 
        // own constructor (which call InitializeComponent()) this is as it 
        // should be for classes extending this
        this.Language = XmlLanguage.GetLanguage(CultureInfo.CurrentCulture.IetfLanguageTag);
    }
}

When the user changes the language I then create new instances of any usercontrols that are currently running.

This solved my problem. However, I would still like a way to do this “automatically” (i.e. without having to keep track of any instantiated objects).