Collation problem after form submission - no Umlaute

I have setup a website with a simple form to subscribe to a newsletter. --> https://www.praxispeer.at/kontakt

Unfortunatly, the success page won’t display the german umlatue (ü,ä,…). Is this a problem on my side or what can I do to fix this?

hi chaollin, i responded in your other thread:

so i am going to close this one.