<Window x:Class="Testsv2343.Window1"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    Title="Window1" Height="310" Width="300">
    <StackPanel Margin="10">
        <Border Background="#ddd" CornerRadius="5" Padding="10">
            <ContentControl x:Name="TheForm"/>
        </Border>
        <StackPanel Orientation="Horizontal">
            <StackPanel HorizontalAlignment="Left" Margin="0 5 5 5">
                <Button Content="English" Click="Button_Click_English"/>
            </StackPanel>
            <StackPanel HorizontalAlignment="Left" Margin="0 5 5 5">
                <Button Content="German" Click="Button_Click_German"/>
            </StackPanel>
        </StackPanel>
        <TextBlock Text="{Binding Message}"/>
    </StackPanel>
</Window>

using System.Windows;
using System.Windows.Controls;
using System.ComponentModel;

namespace Testsv2343
{
    public partial class Window1 : Window, INotifyPropertyChanged
    {
        #region ViewModelProperty: Message
        private string _message;
        public string Message
        {
            get
            {
                return _message;
            }

            set
            {
                _message = value;
                OnPropertyChanged("Message");
            }
        }
        
        private ScrollViewer scrollViewer;
        private double scrollBarPosition = 0;

        private string englishLine = "this is line ";
        private string germanLine = "das ist Zeile ";

        public Window1()
        {
            InitializeComponent();
            DataContext = this;

            CreateForm(englishLine);

        }

        #region INotifiedProperty Block
        public event PropertyChangedEventHandler PropertyChanged;

        protected void OnPropertyChanged(string propertyName)
        {
            PropertyChangedEventHandler handler = PropertyChanged;

            if (handler != null)
            {
                handler(this, new PropertyChangedEventArgs(propertyName));
            }
        }
        
        void CreateForm(string text)
        {

            StackPanel sp = new StackPanel();

            for (int i = 0; i < 100; i++)
            {
                TextBlock tb = new TextBlock();
                tb.Text = text + i.ToString();
                sp.Children.Add(tb);
            }

            scrollViewer = new ScrollViewer();
            scrollViewer.Content = sp;
            scrollViewer.Height = 200;
            scrollViewer.ScrollToVerticalOffset(scrollBarPosition);

            TheForm.Content = scrollViewer;
        }

        private void Button_Click_English(object sender, RoutedEventArgs e)
        {
            scrollBarPosition = scrollViewer.VerticalOffset;
            CreateForm(englishLine);
        }

        private void Button_Click_German(object sender, RoutedEventArgs e)
        {
            scrollBarPosition = scrollViewer.VerticalOffset;
            CreateForm(germanLine);
        }

    }
}