Strange behaviour of Table of contents if there are some Greek words inside the text

Question

Referring to this thread: Subsection titles (and not only) alignement with titletoc, I've a strange behaviour in a specific case. Please, consider the following code:

\documentclass[a4paper,twoside,11pt]{report}
\usepackage{fontspec}
\setmainfont{EB Garamond}
\usepackage{polyglossia}
\setmainlanguage[babelshorthands=true]{italian}
\PolyglossiaSetup{italian}{indentfirst=false}
\setotherlanguage[variant=polytonic]{greek}
\newfontfamily\greekfont[Scale=MatchLowercase]{GFS Didot}
\usepackage{microtype}
\frenchspacing
\usepackage{lipsum}

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

\usepackage{titlesec,titletoc}
\makeatletter
\contentsmargin[-1.55em]{1.55em}
\makeatother

\titlecontents{chapter}
  [3em]
  {\vspace*{\baselineskip}\mdseries}
  {\contentslabel[\hfill\thecontentslabel]{3em}\enspace}
  {\hspace*{0.5em}}
  {\hspace*{0.5em}}
  []

\titlecontents{section}
  [3em]
  {\vspace*{\baselineskip}\mdseries}
  {\contentslabel[\hfill\thecontentslabel]{3em}\enspace}
  {}
{\hfill\llap{\makebox[\dimexpr\linewidth-1.3pc][l]{\makebox[1pc][r]{\thecontentspage}}}}
  []

\titlecontents*{subsection}
  [3.525em]
  {\footnotesize}
  {}
  {}
  {,~\thecontentspage}
  [~--~]
  []

\titleformat{\chapter}[display]
  {\normalfont\fontsize{11pt}{12pt}\selectfont}{\thechapter}{0pt}{}
\renewcommand\thesection{\arabic{section}}
\titleformat{\section}
  {\normalfont\fontsize{11pt}{12pt}\selectfont}{\thesection}{1em}{}
\titleformat{\subsection}
  {\normalfont\fontsize{11pt}{12pt}\selectfont\itshape}{\phantom{\thesection}}{1em}{}
\titlespacing{\chapter}{0pt}{0pt}{3cm}

\renewcommand{\thechapter}{\scshape\roman{chapter}}
\renewcommand{\thesection}{\arabic{section}.}

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

\begin{document}

\tableofcontents

\chapter{Premessa}
\section{Section One}
\subsection{Plato}
\lipsum[1]

\begin{greek}ῥητοτορική τέχνη\end{greek}

\lipsum[2]

\subsection{Aristoteles}
\lipsum[1]

\begin{greek}ῥητοτορική τέχνη\end{greek}

\lipsum[2]

\subsection{A Title a bit longer}
\lipsum[1]

\begin{greek}ῥητοτορική τέχνη\end{greek}

\lipsum[2]

\subsection{Etimo}
La retorica è l'arte di persuadere mediante i discorsi. Il termine deriva dal
latino \emph{rhetorica} (\emph{ars}), mutuato a sua volta dal greco
\begin{greek}ῥητοτορική τέχνη\end{greek}, espressione che indica l'arte del
parlare in pubblico (\begin{greek}ῥήτωρ\end{greek}, ossia colui che parla in
a sua volta deriva dalla radice del verbo \begin{greek}εἴρω\end{greek}, «io
dico».

\subsection{Retorica e linguaggio}
Nel corso dei secoli i teorici si sono impegnati a individuare i vari elementi e
organizzarli in una tassonomia generale, senza però mai raggiungere una
classificazione condivisa.[\begin{greek}ῥητοτορική τέχνη\end{greek}] Questo
ingente numero di trattati, ha contribuito non poco alla stessa decadenza della
retorica.

\subsection{Evoluzione della retorica}
\lipsum[1]

\end{document}

Where in the text there is \begin{greek}...\end{greek}an anomalous space (asymmetrical and greater than necessary) is produced in the Table of contents, as in the pic under:

By eliminating the Greek, everything returns to normal. I don't understand the reason of this little trouble.

How is it possible to solve, for I need to have greek text? Thanx

Answer 1

The issue is due to the fact that each greek environment in the document writes two lines in the auxiliary files, including .toc, namely

\select@language{greek}
\select@language{italian}

These confuse the reading of the file and introduce two spaces.

You can cure this by asking LaTeX to read the .toc file without taking into account end-of-lines.

On the other hand, using \foreignlanguage for short inserts in a different language is certainly preferable. There is a shorthand for this with polyglossia, namely

\textgreek{ῥητοτορική τέχνη}

I'd also recommend defining a new environment like

\newenvironment{greek*}[1][]
  {\begin{otherlanguage*}[#1]{greek}}
  {\end{otherlanguage*}}

for longer passages in Greek, if needed.

In the code I reshaped your preamble to separate package loading and settings. I left the \begin{greek}...\end{greek}, except at one place for showing that \textgreek works.

\documentclass[a4paper,twoside,11pt]{report}
\usepackage{fontspec}
\usepackage{polyglossia}
\usepackage{microtype}
\usepackage{titlesec,titletoc}

\usepackage{lipsum}

%%% patch \@starttoc to ignore end lines
\makeatletter
\patchcmd{\@starttoc}{\begingroup}{\begingroup\endlinechar=-1\relax}{}{}
\makeatother

\setmainfont{EB Garamond}
\setmainlanguage[babelshorthands=true]{italian}
\PolyglossiaSetup{italian}{indentfirst=false}
\setotherlanguage[variant=polytonic]{greek}
\newfontfamily\greekfont[Scale=MatchLowercase]{GFS Didot}
\frenchspacing

\contentsmargin[-1.55em]{1.55em}

\titlecontents{chapter}
  [3em]
  {\vspace*{\baselineskip}\mdseries}
  {\contentslabel[\hfill\thecontentslabel]{3em}\enspace}
  {\hspace*{0.5em}}
  {\hspace*{0.5em}}
  []

\titlecontents{section}
  [3em]
  {\vspace*{\baselineskip}\mdseries}
  {\contentslabel[\hfill\thecontentslabel]{3em}\enspace}
  {}
  {\hfill\llap{\makebox[\dimexpr\linewidth-1.3pc][l]{%
   \makebox[1pc][r]{\thecontentspage}}}}
  []

\titlecontents*{subsection}
  [3.525em]
  {\footnotesize}
  {}
  {}
  {,~\thecontentspage}
  [~--~]
  []

\titleformat{\chapter}[display]
  {\normalfont\fontsize{11pt}{12pt}\selectfont}{\thechapter}{0pt}{}
\renewcommand\thesection{\arabic{section}}
\titleformat{\section}
  {\normalfont\fontsize{11pt}{12pt}\selectfont}{\thesection}{1em}{}
\titleformat{\subsection}
  {\normalfont\fontsize{11pt}{12pt}\selectfont\itshape}{\phantom{\thesection}}{1em}{}
\titlespacing{\chapter}{0pt}{0pt}{3cm}

\renewcommand{\thechapter}{\scshape\roman{chapter}}
\renewcommand{\thesection}{\arabic{section}.}

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

\begin{document}

\tableofcontents

\chapter{Premessa}
\section{Section One}
\subsection{Plato}
\lipsum[1]

\textgreek{ῥητοτορική τέχνη}

\lipsum[2]

\subsection{Aristoteles}
\lipsum[1]

\begin{greek}ῥητοτορική τέχνη\end{greek}

\lipsum[2]

\subsection{A Title a bit longer}
\lipsum[1]

\begin{greek}ῥητοτορική τέχνη\end{greek}

\lipsum[2]

\subsection{Etimo}
La retorica è l'arte di persuadere mediante i discorsi. Il termine deriva dal
latino \emph{rhetorica} (\emph{ars}), mutuato a sua volta dal greco
\begin{greek}ῥητοτορική τέχνη\end{greek}, espressione che indica l'arte del
parlare in pubblico (\begin{greek}ῥήτωρ\end{greek}, ossia colui che parla in
a sua volta deriva dalla radice del verbo \begin{greek}εἴρω\end{greek}, «io
dico».

\subsection{Retorica e linguaggio}
Nel corso dei secoli i teorici si sono impegnati a individuare i vari elementi e
organizzarli in una tassonomia generale, senza però mai raggiungere una
classificazione condivisa.[\begin{greek}ῥητοτορική τέχνη\end{greek}] Questo
ingente numero di trattati, ha contribuito non poco alla stessa decadenza della
retorica.

\subsection{Evoluzione della retorica}
\lipsum[1]

\end{document}

In the next release of LaTeX, planned for the beginning of 2019, the issue should vanish, because all lines written to the auxiliary files by \addtocontents will basically be ended by a %.