\documentclass[numbers=noenddot]{scrbook}
\renewcommand*{\chapterpagestyle}{empty}
\renewcommand*{\partpagestyle}{empty}
\usepackage{fontspec}
\usepackage{polyglossia}
\setdefaultlanguage[spelling=new, latesthyphen=true, babelshorthands=true]{german}
\setmainfont{EB Garamond}
\setsansfont{EB Garamond}
\usepackage[series={A,B},noend,noeledsec]{reledmac}
\usepackage{reledpar}
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\sethangingsymbol{\protect\hfill}
\parindent=0pt

\begin{document}
\subsection{Text and Translastion}
Bla bla bla and \dots
\begin{pages}
\beginnumbering
\begin{Leftside}
\begin{itshape}
\begin{astanza}\subsubsection*{Text} XXX XXX XXX\dots  XXX XXX XXX XXX XXX XXX XXX XXX XXX XXX XXX XXX XXX XXX XXX \dots XXX XXX XXX XXX XXXXXX. &
XXX \& \end{astanza}
\end{itshape}
\endnumbering
\end{Leftside}

\begin{Rightside}
\beginnumbering
\begin{astanza}\subsubsection*{Translation} XXX XXX XXX XXX XXX XXX XXX XXX XXX XXX XXX \dots XXX XXX XXX XXX XXXXXXXXX XXXXXXXXX XXX XXX XXX XXX XXX XXX XXX XXX XXX XXX XXX \dots XXX XXX XXX XXX XXXXXX. &
XXX \& \end{astanza}
\endnumbering
\end{Rightside}
\end{pages}
\Pages
\end{document}