XeLaTeX, xindy, imakeidx "Could not find file "tex/inputenc/utf8.xdy"

Question

I'm trying to use XeLaTeX, imakeidx and xindy for a german book with multiple indexes. Based on an answer on this page, (which works) I tried to switch to xelatex and imakeidx. Calling

xelatex --shell-escape test.tex

on this file test.tex:

\documentclass{article}
\usepackage{xltxtra}
\usepackage[xindy]{imakeidx}
\makeindex[options=-M texindy -L german-duden -C utf8]
\begin{document}
üäö
start 
\index{a}\index{b}\index{ä}\index{ü}\index{ÖÖ}
end
\printindex
\end{document}

gives me the error message:

(require "tex/inputenc/utf8.xdy") ERROR: Could not find file "tex/inputenc/utf8.xdy" !

Leaving out xindy option "-C utf8" gives me an index with alll umlauts sorted under "O".

I just discovered that xindy does work when run separately, without being started from within xelatex per imakeidx, but from the command prompt:

 $ xindy -M texindy -C utf8 -L german-duden test.idx

No nagging and no mention of "utf8.xdy" either.

Answer 1

Calling \makeindex[program=truexindy,...] works.

\documentclass{article}
\usepackage{fontspec}
\usepackage{imakeidx}
\makeindex[program=truexindy,options=-M texindy -L german-duden -C utf8]
\begin{document}
üäö
start
\index{a}\index{b}\index{ä}\index{ü}\index{ÖÖ}
end
\printindex
\end{document}