\documentclass{scrbook}
\usepackage[series={A,B},noend,noeledsec]{reledmac}
\usepackage{reledpar}
\setstanzaindents{1,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0,0}

\parindent=0pt

\begin{document}
\begin{pages}
\beginnumbering
\begin{Leftside}
\begin{astanza}[\subsubsection{Text}] XXX XXX XXX. &
XXX \& \end{astanza}
\endnumbering
\end{Leftside}

\begin{Rightside}
\beginnumbering
\begin{astanza}[\subsubsection{Translation}] XXX. &
XXX \& \end{astanza}
\endnumbering
\end{Rightside}
\end{pages}
\Pages

\end{document}
