newwrite and read in with umlauts

Question

I write the file out.csv, which contains umlauts and tried to read it in. How can I make this work?

\documentclass[margin=5pt, varwidth]{standalone}
\usepackage{pgfplotstable}
\pgfplotsset{compat=newest}
\begin{document}
\newwrite\out
\immediate\openout\out=out.csv
\foreach[count=\n from 0] \word in {ä, ö, ü, ß, x, y}{
\immediate\write\out{\n; \word }% works not
%\immediate\write\out{\n; \detokenize{\word} }% works not too
}
\immediate\closeout\out
\input{out.csv}
\pgfplotstableread[col sep=semicolon, header=false]{out.csv}{\mytable}
\pgfplotstabletypeset[string type]{\mytable}
\end{document}

Answer 1

You need to expand \word before applying \detokenize

\immediate\write\out{\n: \detokenize\expandafter{\word}}

There's no need to do \expandafter\detokenize\expandafter{\word}, because \detokenize expands tokens while looking for {.

For more complex applications, you might try \protected@iwrite, see https://tex.stackexchange.com/a/596328/4427

Answer 2

As suggested by Ulrike Fischer in chat, another possibility is to use @egreg \protected@iwrite:

\documentclass{article}
\usepackage{pgfplotstable}
\pgfplotsset{compat=newest}
\makeatletter
\long\def\protected@iwrite#1#2#3{%
  \begingroup
  #2%
  \let\protect\@unexpandable@protect
  \edef\reserved@a{\immediate\write#1{#3}}%
  \reserved@a
  \endgroup
  \if@nobreak\ifvmode\nobreak\fi\fi
}
\newcommand{\mywrite}[2]{\protected@iwrite#1{}{#2}}%
\makeatother
\begin{document}
\newwrite\out
\immediate\openout\out=out.csv
\foreach[count=\n from 0] \word in {ä, ö, ü, ß, x, y}{
    \mywrite\out{\n; \word ; \word}% now it works
}
\immediate\closeout\out
\input{out.csv}
\pgfplotstableread[col sep=semicolon, header=false]{out.csv}{\mytable}
\pgfplotstabletypeset[string type]{\mytable}
\end{document}