\documentclass[paper=a5]{scrartcl}
\usepackage[ngerman]{babel}
%StartVisiblePreamble
\usepackage{makeidx}\makeindex
\newcommand\Index[1]{\index{#1}#1}
%StopVisiblePreamble
\usepackage{multicol}
\makeatletter
\def\theindex{%    only for demonstration
  \newpage
  \section*{\indexname}
  \begin{multicols}{2}
  \parskip\z@ \@plus .3\p@\relax \parindent\z@
  \let\item\@idxitem}
\def\endtheindex{\end{multicols}}
\makeatother
\pagestyle{empty}
\begin{document}
Sorted with \verb|-l DE|

\Index{Österreich} \Index{Öresund}
\Index{Ostern} \Index{Ober}
\Index{Oberin} \Index{Österreich}
\Index{Öresund} \Index{Ostern}
\Index{Ober} \Index{Oberin}
\Index{Obstler} \Index{Öl}
\Index{ölen} \Index{Ödem}
\Index{Oligarch} \Index{Oder}
\Index{oder} \index{Fluss!Oder}
\index{Oder|seealso{Fluss}}
\Index{Göbel} \Index{Goethe}
\Index{Göthe} \Index{Götz}
\Index{Goldmann}

\printindex
\end{document}
