Invalid Answer pop-up in Storyline Quizzes

Hi there!

I've been building a storyline project in German and as such need to replace/edit as many default/built-in buttons as possible with German translations. 

My only problem has been finding where the "Invalid Answer" pop-up is located so I can either edit or replace it. Ideally I don't want to have to remove/replace the submit button at this stage - is it possible to keep it AND have a custom invalid answer box?

Thanks in advance!