\listfiles
\documentclass{article}

\usepackage{ginpenc}
\usepackage[latin1]{inputenc}
\usepackage[english,ngerman]{babel}
\usepackage{makeidx}

\makeindex

\providecommand\inputenc{??}

\begin{document}
Please have a look into the file \jobname.idx.
Here, the entry written in German should be typed with \verb|"u| while
the English version is typed with \verb|\"u|.

\typeout{\languagename:}
\typeout{* Input encoding: `\inputenc'}

\index{Rüber (ger)}

\inputencoding{cp850}
\typeout{* Input encoding: `\inputenc'}
\inputencoding{latin1}

\selectlanguage{english}
\typeout{\languagename:}
\typeout{* Input encoding: `\inputenc'}

\index{Rüber (eng)}

\inputencoding{cp850}
\typeout{* Input encoding: `\inputenc'}
\printindex

\end{document}
