text comparison for Umlaut

I need to compare the input text with a fixed text.

The problem is there could be Umlaut in the text, such as ü,ä,ö.

But it seems that wm input field doesn’t support umlaut, and show ? for all of them.

so I think there will be problem if the fixed text is Tür but the input text will be T?r.

So what can I do to avoid that?