one button + multiple TextBox's = problem?

Got a form with several TextBox'es for the user to enter info. Sometimes the words to be entered will be in German, which has several special characters not present in English.

What I'd like to do is have small buttons at the bottom of the form, one for each special character (ä, ö, ü, ß) so that if I need to enter the word "grün" I can type the first two characters in the textbox, click on the button with the "ü" on it and have that letter appear at the end of the first two characters in the textbox, then after clicking have the focus returned to the textbox so I can finish typing.

Any ideas how to accomplish this?

Thanks!

I thought that the German Windows version (regionalization), would automatically handle the need for Germans to enter in ü and such. Is that not part of the keyboard layout for them? And if so, does that not make this a non-issue to begin with?

Yes, but only those who have that specific version of Windows AND a German keyboard would have an easy time of entering these characters. For everyone else, you have to first enable the German text service in Windows, use <CTRL+SHIFT> (or go through the control panel) to switch back and forth between a German and English virtual keyboard, and even then these characters replace several standard punctuation keys. In other words it's awkward, so I thought that just having the 4 characters as buttons may make the data entry process easier for some people.