\documentclass{article}
\usepackage{amsmath}
\usepackage{luapersian}
\settextfont{Yas}
\setdigitfont{Yas}
\directlua { tex.enableprimitives('',{'mathdir'})}
\makeatletter
\newenvironment{RTLcases}{%
  \matrix@check\RTLcases\env@RTLcases
}{%
  \endarray\right.%
}
\def\env@RTLcases{%
  \let\@ifnextchar\new@ifnextchar
  \left\rbrace
  \def\arraystretch{1.2}%
  \array{@{}l@{\quad}l@{}}%
}
\makeatother
\begin{document}
\mathdir TRT
\[
\text{آدم}
\begin{RTLcases}
\text{مرد}\\
\text{زن}
\end{RTLcases}
\]
\end{document}