Posted by ChrLipp on Sep 10, 2013; 6:29am
URL: https://discuss.asciidoctor.org/Encoding-of-special-German-Umlaut-characters-in-html-backend-tp548p551.html

You are right, my mistake.
I missed the

<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">

in the generated HTML.

Thanks for your answer.