Too bad the source code of that beautiful toy is nowhere to be found - I'd gladly provide a patch that teaches it about the umlauts which it unfortunately left alone in your piece of art you created here <3
It's trivial to dump the tables at least. Just enter all printable ascii characters :). The umlauts would be by first fully decomposing the string down to letters+combining characters, right?
I have a tool to make this text, though I'll admit I never even thought about decomposing inputs like ΓΌ and then recomposing them after Fraktur-izing.