XeTeX with polyglossia template (for greek, french and english)

polyglot-xetex-template.tex

\documentclass{article}

\usepackage{fontspec, polyglossia}

\setmainlanguage{french}
\setotherlanguages{english, greek}
\newfontfamily\greekfont{Times New Roman}

\begin{document}

\textgreek{Καλημέρα κόσμε!}
\textenglish{Hello world!}
\textfrench{Bonjour tout le monde!}

\end{document}