\documentclass{article}
\usepackage[greek,english]{babel}
\ifx\Umathchar\undefined
\usepackage[utf8]{fontenc}
\else
\usepackage{fontspec}
\fi
\ifx\XeTeXcharclass\undefined\else
\makeatletter
\long\def\showhyphens#1{%
\setbox0\vbox{%
\usefont{TU}{lmr}{m}{n}% needs to be an OT font
\hsize 1sp
\hbadness\@M
\hfuzz\maxdimen
\everypar={}%
\leftskip
\rightskip\z@skip
\pretolerance\m@ne
\interlinepenalty\z@
\clubpenalty\z@
\widowpenalty\z@
\brokenpenalty1127 % unlikely number