Markup Extension in Data Trigger

To translate my WPF application I use a Markup extension which returns a Binding object. This allows me to switch the language while the application is running. I use this Markup like this:

<TextBlock Text="{t:Translate 'My String'}" />"

I would like to change a Buttons text through a data Trigger:

<Button>
    <Button.Style>
        <Style TargetType="{x:Type Button}">
            <Setter Property="Template">
                <Setter.Value>
                    <!-- Custom control template, note the TextBlock formating -->
                    <ControlTemplate TargetType="{x:Type Button}">
                        <Grid x:Name="ContentHolder">
                            <ContentPresenter TextBlock.Foreground="Red" TextBlock.FontWeight="Bold" />
                        </Grid>
                    </ControlTemplate>
                </Setter.Value>
            </Setter>
            <!-- Custom text triggered by Data Binding... -->
            <Style.Triggers>
                <DataTrigger Binding="{Binding MessageRowButton}" Value="Retry">
                    <Setter Property="Button.Content" Value="{t:Translate Test}" />
                </DataTrigger>
                <DataTrigger Binding="{Binding MessageRowButton}" Value="Acknowledge">
                    <Setter Property="Button.Content" Value="{t:Translate Test}" />
                </DataTrigger>
            </Style.Triggers>
        </Style>
    </Button.Style>
</Button>

This leads to the following exception:

A 'Binding' cannot be set on the 'Value' property of type 'Setter'. A 'Binding' can only be set on a DependencyProperty of a DependencyObject.

Ok, this make sense to me. I tried to define TextBlock in my Resource and use {StaticResource MyResource} in the DataTrigger's Setter Value. But when I do this, the style of my Button is not correctly applied...

How can I work with my markup extension and change text on the button without destring the ability to style the string inside the button?

Try returning the markup extension itself (this) if the target (IProvideValueTarget.TargetObject) is a setter. It will be reevaluated when the style is applied to an actual element.

public object ProvideValue(IServiceProvider serviceProvider)
{
    var pvt = service.GetService(typeof(IProvideValueTarget)) as IProvideValueTarget;
    if (pvt.TargetObject is Setter)
        return this;

    ...
}