Allowing users to type special characters in text entry boxes

Hello,

I'm developing a course designed to help people learn foreign languages. This includes providing a variety of different exercises, including one using text entry boxes where people have to fill in the blanks (as in the attached sample slide).

The problem is that English keyboards obviously don't give users ready access to foreign characters, such as "ä, ö, ü or ß". So I have been trying to figure out a solution to help circumvent this problem.

So I created buttons, one for each of these special characters. The idea is that users input text via their normal keyboard but when they need access to a special character, they can use one of these buttons on the slide. I have seen this function in other e-Learning programmes, but have not been able to replicate it myself in Articulate.

I know that I can use variables to assign a particular text to a text entry box. But this will delete any text that might have already been entered. So what I need is a function that will simply "add" these special characters to a word that is being entered by a student. Any thoughts?

Thanks!