\documentclass{scrartcl}
\usepackage[extrafootnotefeatures]{xepersian}
\renewcommand\foottextfont{\footnotesize\bfseries}
\renewcommand\LTRfoottextfont{\footnotesize\sffamily\bfseries}
% also see extrafootnotefeatures-xepersian.def
\paragraphfootnotes
\begin{document}
\LTRfootnote{Hello}\footnote{سلام}
\end{document}