Redirect to URL with umlauts or accents via .htaccess

To redirect to a new URL that contains diacritics via .htaccess, what is the correct and safe way?

• Can I somehow set the .htaccess file to UTF-8 and just use the non-ASCII characters, e.g.:
  redirect 301 / http://www.bücher.ch/

• Need I use the ACE string instead, e.g.:
  redirect 301 / http://www.xn--bcher-kva.ch/

• Is urlencode the way to go? I tried the following without success:
  redirect 301 / http://www.b%C3%BCcher.ch/

For context, the following page on internationalized domain names (IDN) has a section about the technical solution to include accents and umlauts in domains.

In the domain part, you must use ASCII Compatible Encoding (ACE). In the rest of the URL, you use urlencode. So, in .htaccess…

http://www.bücher.ch/schöne/

…needs to be written as…

http://www.xn--bcher-kva.ch/sch%C3%B6ne/