\documentclass{beamer}
\usepackage{ptext}
\usefonttheme{serif}
\usepackage{xepersian}
\settextfont{Yas}
\title{یک اسلاید نمونه}
\subtitle{زیرعنوان اسلاید}
\author{نام نویسنده}
\raggedleft
\makeatletter
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\makeatother
\providetranslation{Theorem}{قضیه}
\providetranslation{Definition}{تعریف}
\providetranslation{Example}{مثال}
\begin{document}

\begin{frame}
\ptext[1]
\begin{definition}
این یک تعریف است
\end{definition}
\begin{theorem}
این یک قضیه است
\end{theorem}

\begin{proof}
این یک آثبات است.
\end{proof}

\begin{example}
این یک مثال است
\end{example}
\end{frame}

\end{document}