Empty textbox on mousclick in combination with language change in WPF - wpf

Question

I have a textbox with a default text. When I focus the textbox it is cleared so I can write, and if I unfocus without writing anything the default text reappears.
I also have two radiobuttons for selecting the language. The languages are provided as xaml resourcefiles and the default text in the textbox is connected to that using DynamicResource.
My problem is that the language change only work as long as I haven't focused the textbox. If I focus the textbox and then unfocus it without changing anything, the textbox no longer changes language.
I'm guessing that is because once it's changed (cleared) it's no longer linked to the dynamic resource, because WPF considers my onfocus changes as user input, but I can't figure out how to get around that and make it change language even if I've clicked the textbox.
The second textbox don't have any focus behaviour and in that one the language change works as it should, i.e. it changes the language as long as I haven't actually written something.
MainWindow xaml:
<Window x:Class="Textbox_langauge_buggseek.MainWindow"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
xmlns:local="clr-namespace:Textbox_langauge_buggseek"
mc:Ignorable="d"
Title="MainWindow" Height="350" Width="525">
<Grid>
<TextBox x:Name="TextBox" HorizontalAlignment="Left" Height="46" Margin="84,55,0,0" TextWrapping="Wrap" Text="{DynamicResource ResourceKey=TB}" VerticalAlignment="Top" Width="334" GotFocus="TextBox_GotFocus" LostFocus="TextBox_LostFocus"/>
<TextBox x:Name="TextBox_Copy" HorizontalAlignment="Left" Height="46" Margin="84,123,0,0" TextWrapping="Wrap" Text="{DynamicResource ResourceKey=TB}" VerticalAlignment="Top" Width="334"/>
<RadioButton x:Name="En" Content="En" GroupName="Lang" HorizontalAlignment="Left" Margin="391,216,0,0" VerticalAlignment="Top" Checked="En_Checked" IsChecked="True"/>
<RadioButton x:Name="Se" Content="Se" GroupName="Lang" HorizontalAlignment="Left" Margin="391,234,0,0" VerticalAlignment="Top" Checked="Se_Checked"/>
</Grid>
</Window>
MainWindows cs:
using System;
using System.Windows;
using System.Windows.Controls;
namespace Textbox_langauge_buggseek
{
public partial class MainWindow : Window
{
public MainWindow()
{
InitializeComponent();
SetLanguageDictionary();
}
//*****************************************************************************************
private void TextBox_GotFocus(object sender, RoutedEventArgs e)
{
TextBox box = sender as TextBox;
box.Text = box.Text == (string)this.Resources["TB"] ? string.Empty : box.Text;
}
private void TextBox_LostFocus(object sender, RoutedEventArgs e)
{
TextBox box = sender as TextBox;
box.Text = box.Text == string.Empty ? (string)this.Resources["TB"] : box.Text;
}
//*****************************************************************************************
private void En_Checked(object sender, RoutedEventArgs e)
{
SetLanguageDictionary("En");
}
private void Se_Checked(object sender, RoutedEventArgs e)
{
SetLanguageDictionary("Se");
}
//*****************************************************************************************
private void SetLanguageDictionary(string language = "En")
{
ResourceDictionary dict = new ResourceDictionary();
switch (language)
{
case "Se":
dict.Source = new Uri("..\\Resources\\Se.xaml", UriKind.Relative);
break;
default:
dict.Source = new Uri("..\\Resources\\En.xaml", UriKind.Relative);
break;
}
this.Resources.MergedDictionaries.Add(dict);
}
}
}
En language xaml:
<ResourceDictionary
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:system="clr-namespace:System;assembly=mscorlib">
<system:String x:Key="TB">Text in the TextBox!</system:String>
</ResourceDictionary>
Se language xaml:
<ResourceDictionary
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:system="clr-namespace:System;assembly=mscorlib">
<system:String x:Key="TB">Text i textrutan!</system:String>
</ResourceDictionary>

Answer 1

Yes, when you set TextBox.Text in codebehind, the text does not know anymore that it has to take a value from the Rersource. To avoid it you can change the text using pure XAML, with Triggers.
Remove TextBox's event handlers and add a style like this:
<TextBox x:Name="TextBox" HorizontalAlignment="Left" Height="46" Margin="84,55,0,0" TextWrapping="Wrap" VerticalAlignment="Top" Width="334">
<TextBox.Style>
<Style TargetType="{x:Type TextBox}">
<Style.Triggers>
<Trigger Property="IsFocused" Value="true">
<Setter Property="Text" Value="" />
</Trigger>
<Trigger Property="IsFocused" Value="false">
<Setter Property="Text" Value="{DynamicResource ResourceKey=TB}" />
</Trigger>
</Style.Triggers>
</Style>
</TextBox.Style>
</TextBox>