DatePicker: how can I translate its contents?

Hi there,

Due to my WPF app run both english and spanish, the only thing to translate now is the literal "Select a date" on DatePicker control. This text appears by default.

Have not idea how can I access from run-time and change it!!

Help!!

XAML:

<DatePicker x:Name="FCaducidad" Grid.Column="1" HorizontalAlignment="Left" Margin="10,36,0,0"
           FontFamily="Trebuchet Ms"
       FontSize="14" Grid.Row="1" VerticalAlignment="Top" Height="25" Grid.ColumnSpan="2" Width="184" Grid.RowSpan="3"/>

Thanks a lot for your thoughts

Primary platform is Windows 7 Ultimate 64 bit along with VS 2012/Sql2k8 for WPF/SilverLight projects.