some doubts about polyglossia

Question

This is the mwe from which the error can be seen. If \begin{otherlanguage}{french} and \end{otherlanguage}, I get Extra }, or forgotten \endgroup error.

With \selectlanguage{french} no error and it doesn't need the end command so in this case I don't know if in the right part of the chunk the Italian language has been selected.

With \textfrench{......} no error but I think this is not the right command because of the manual: "the command becomes available for short insertions of text in that language".

Given that I have many hundreds of reledmac chunks and given that I have already set up all the left side part of the chunks with the couple "begin language", "end language", I would like to know if is my the fault or polyglossia fault.

\documentclass[a4paper,twoside,openright,10pt,final]{memoir}
\usepackage{polyglossia}
\usepackage[series={A,B},noledgroup,noend,noquotation,noeledsec]{reledmac}
\usepackage[]{reledpar}
\setgoalfraction{.95}
\linenumincrement*{1}
\firstlinenum*{0}
\setRlineflag{d}
\setlength{\Lcolwidth}{66mm} 
\setlength{\Rcolwidth}{66mm} 
\AtBeginPairs{\sloppy}
\usepackage{fontspec}
\setmainlanguage{italian}
\setotherlanguage[automaticspacesaroundguillemets=false]{french}
\setotherlanguage{hebrew}
\setstocksize{303mm}{216mm}
\setpagecc{297mm}{210mm}{*}
\settypeblocksize{220mm}{136mm}{*}
\setlrmargins{35mm}{*}{1}
\setulmargins{30mm}{*}{1.4142}
\setheadfoot{10mm}{10mm}
\setmarginnotes{8mm}{25mm}{10pt}
\checkandfixthelayout

\begin{document}

    \begin{pairs}
        \begin{Leftside} 
            \beginnumbering
                \pstart
%\selectlanguage{french}
\begin{otherlanguage}{french}
%\textfrench{
Le français est une langue indo-européenne de la famille des langues romanes. Le français s'est formé en France (variété de la « langue d’oïl », qui est la langue de la partie septentrionale du pays). Le français est déclaré langue officielle en France en 1539.
%}
\end{otherlanguage}
                \pend
            \pausenumbering
        \end{Leftside}

        \begin{Rightside} 
            \beginnumbering
                \pstart
%\selectlanguage{italian}
Il francese è una lingua indo--europea appartenente alla famiglia delle lingue neo--latine. Il francese si è formato in Francia (varietà della lingua d'oil, che è la lingua della parte settentrionale del paese). Il francese è stato dichiarato lingua ufficiale in Francia nel 1539.
                \pend
            \pausenumbering
        \end{Rightside}
    \end{pairs}
\Columns

\end{document}

Answer 1

With the most recent update to polyglossia, the otherlanguage environment has been slightly changed.

The reledmac package changes the same environment's definition in order to do other necessary things, but hasn't yet been updated to respect the change.

Solution: patch the version of reledmac to add the required code.

\documentclass[a4paper,twoside,openright,10pt,final]{memoir}
\usepackage{polyglossia}
\usepackage[series={A,B},noledgroup,noend,noquotation,noeledsec]{reledmac}
\usepackage[]{reledpar}
\usepackage{xpatch}

\setgoalfraction{.95}
\linenumincrement*{1}
\firstlinenum*{0}
\setRlineflag{d}
\setlength{\Lcolwidth}{66mm} 
\setlength{\Rcolwidth}{66mm} 
\AtBeginPairs{\sloppy}
\usepackage{fontspec}
\setmainlanguage{italian}
\setotherlanguage[automaticspacesaroundguillemets=false]{french}
\setotherlanguage{hebrew}
\setstocksize{303mm}{216mm}
\setpagecc{297mm}{210mm}{*}
\settypeblocksize{220mm}{136mm}{*}
\setlrmargins{35mm}{*}{1}
\setulmargins{30mm}{*}{1.4142}
\setheadfoot{10mm}{10mm}
\setmarginnotes{8mm}{25mm}{10pt}
\checkandfixthelayout

\makeatletter
\AtBeginDocument{%
  \xpretocmd{\otherlanguage}{\xpg@set@group@aux}{}{}% \xpg@set@group@aux is missing in reledmac
}
\makeatother

\begin{document}

    \begin{pairs}
        \begin{Leftside} 
            \beginnumbering
                \pstart
\begin{otherlanguage}{french}
Le français est une langue indo-européenne de la famille des langues romanes. 
Le français s'est formé en France (variété de la « langue d’oïl », qui est la 
langue de la partie septentrionale du pays). Le français est déclaré langue 
officielle en France en 1539.
\end{otherlanguage}
                \pend
            \pausenumbering
        \end{Leftside}

        \begin{Rightside} 
            \beginnumbering
                \pstart
Il francese è una lingua indo--europea appartenente alla famiglia delle lingue 
neo--latine. Il francese si è formato in Francia (varietà della lingua d'oil, 
che è la lingua della parte settentrionale del paese). Il francese è stato 
dichiarato lingua ufficiale in Francia nel 1539.
                \pend
            \pausenumbering
        \end{Rightside}
    \end{pairs}
\Columns

\end{document}