Markup Extension in Data Trigger - wpf

Question

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?

Answer 1

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;
...
}