I am trying to redirect requests from a umlaut domain to another domain.

My following code works with ANY other domain, but not umlaut:

<IfModule mod_rewrite.c>
  RewriteCond %{HTTPS} !=on
  RewriteCond %{HTTP_HOST} ^(www\.)?frankfurter-flöhe\.de/$ [NC]
  RewriteRule ^ http://kinderkultur-frankfurt.de/frankfurter-floehe-theaterprogramm.html [R=301,L]
</IfModule>

However, when I call the umlaut domain and copy it from google chromes address bar after that, I get this:

http://xn--frankfurter-flhe-zwb.de/

Altough, if I use that obfruscated domain in my htaccess instead of the "real" umlaut domain, it doesn't work either.

Does anybody have an idea how to match that domain?