Wrong displaying of German letters


I have a netlify form integrated on my website and created my own confirmation page.
On this page we have German letters like " ä / ö / ü ".

When I check the live version of my page by just entering the url, the letters are shown correctly.
But when an user gets the confirmation page displayed like this:

Does someone know why this happens and how I can avoid that?

(P.S. At the moment I chose a different spelling of the words so that the Germans can at least read what is written and are not confronted with this kind of “hyroglyphs”.)

My netlify site name is “effervescent-sawine-2c0508”

Thank you and best regards,

That looks like a font issue than a Netlify issue. Please ensure the font that you’re using supports all the glyphs that you wish to use.