\documentclass[12pt]{article} 
\usepackage[no-math]{fontspec}
\defaultfontfeatures{Scale=MatchLowercase}
\setromanfont{Linux Libertine}
\setsansfont{DejaVu Sans}
\setmonofont{DejaVu Sans Mono}
\newfontfamily\arabicfont[Script=Arabic]{Scheherazade}
\newfontfamily\arabicfontsf[Script=Arabic]{DejaVu Sans}
\newfontfamily\arabicfonttt[Script=Arabic]{DejaVu Sans Mono}
\usepackage{polyglossia}
%\tracingall
\setdefaultlanguage{french}
\setotherlanguage{bahasai}
\setotherlanguage{turkish}
\setotherlanguage{ukrainian}
\setotherlanguage{arabic}
\def\showfamily{\fbox{\small\familytype}}
\begin{document}\showfamily

Bonjour! 

\textukrainian{\today}

\textbahasai{\today}

\textturkish{\today}


\newpage
%
Some normal text. \showfamily
\itshape Some italic text.
\scshape Some upshape text. 

\ttfamily some code… \showfamily

\rmfamily Some normal text. \showfamily
\normalfont normal \showfamily

texte «normal». \textit{\textturkish{türkçe metin}}. \textturkish{\textit{türkçe metin}}.

texte «normal». \textit{\begin{turkish} türkçe metin.\end{turkish}} \begin{turkish}\textit{türkçe metin.}\end{turkish}

\textarabic{متن عربي / \today = \Hijritoday}


\sffamily\showfamily

texte «normal». \textbf{\textarabic{\showfamily متن عربي}} \textarabic{\textbf{متن عربي}}

\bfseries
texte «normal». 

\begin{Arabic}\mdseries متن عربي\end{Arabic} 
  
\begin{Arabic}\textmd{متن عربي}\end{Arabic}

\end{document}
