> If it's really Ispell that you are using (not Aspell or Hunspell that
> pretend to be Ispell), then you cannot use UTF-8, because Ispell
> doesn't support it.  You must use 8-bit encoding such as Latin-1.

Ok I used (setq  ispell-program-name "ispell")

I tried now tried out aspell but then I receive 
Debugger entered--Lisp error: (error "Error: The file \"/usr/lib/aspell/deutsch\" can not be opened for reading.")
  signal(error ("Error: The file \"/usr/lib/aspell/deutsch\" can not be opened for reading."))
  error("%s" "Error: The file \"/usr/lib/aspell/deutsch\" can not be opened for reading.")
  ispell-init-process()
  ispell-buffer-local-words()
  ispell-accept-buffer-local-defs()
  flyspell-accept-buffer-local-defs()
  flyspell-word()
  flyspell-post-command-hook()

Hm I think I stick with latin-1.

-- 
I strongly condemn Hamas heinous despicable pogroms/atrocities on Israel
I strongly condemn Putin's war of aggression against Ukraine.
I support to deliver weapons to Ukraine's military. 
I support the EU and NATO membership of Ukraine.