Add TextBox with Spelling Check (SpellCheck) Feature in ASP.Net

You can try this: http://spellchecktextbox.codeplex.com . It uses the WPF control as a base.

1. open the tool project and build it.
2. In your project right click the tool box(I usually do it under general.)
3. Click choose items.
4. Browse to TextBoxSource\obj\Debug
5. Add the DLL ExtendedTextBox.dll

Also If the tool project is in another solution you will need to add the DLL to your references folder as well.

Edit: I just realized you said you wanted German spell check. You will need to change this in the control project. Change:

<TextBoxSpellCheck.IsEnabled="True"Name="theTextBox"AcceptsReturn="True"AcceptsTab="True"Text=""Cursor="IBeam"CaretBrush="#E6000000"/>

to something like

<TextBoxSpellCheck.IsEnabled="True"Name="theTextBox"AcceptsReturn="True"AcceptsTab="True"Text=""Cursor="IBeam"CaretBrush="#E6000000" xml:lang="German Culture Code here"/>