\documentclass{article}
\usepackage{fontspec}
\newfontfamily{\greekfont}{Gentium}
\makeatletter
\typeout{l@greek = \the\l@greek}
\typeout{l@monogreek = \the\l@monogreek}
\typeout{l@polygreek = \the\l@polygreek}
\typeout{l@ancientgreek = \the\l@ancientgreek}
\makeatother
\usepackage{polyglossia}
\setmainlanguage{greek}
% The (*2) line tells Greek should be polytonic.
%\setkeys{greek}{variant=polytonic}
% The (*3) line tells Greek should be ancient.
\setkeys{greek}{variant=ancient}
\begin{document}
\typeout{language = \the\language}
\end{document}
