I want to change the standard enumeration (arabic numbers) in enumeration environment with the greek lowercase alphabet, using enumitem package.
I also use XeLateX engine to compile my document. The problem is that, when I use
\documentclass{article}
\usepackage{fontspec,xgreek,enumitem}
\defaultfontfeatures{Mapping=tex-text}
\setromanfont[Mapping=tex-text]{GFS Artemisia}
\usepackage{polyglossia}
\setdefaultlanguage{english}
\setotherlanguage[variant=modern]{greek}
\begin{document}
\begin{enumerate}[label=\let\textdexiakeraia\relax(\alph*)]
\item bla bla
\item bla bla
\end{enumerate}
\end{document}
I get the following error (from my log file):
! Undefined control sequence.
\labelenumi ->\let \textdexiakeraia
\relax (\alph *)
l.120 ...label=\let\textdexiakeraia\relax(\alph*)]
The control sequence at the end of the top line
of your error message was never \def'ed. If you have
misspelled it (e.g., `\hobx'), type `I' and the correct
spelling (e.g., `I\hbox'). Otherwise just continue,
and I'll forget about whatever was undefined.
LaTeX Info: Redefining \anw@print on input line 121.
LaTeX Font Info: Font shape `EU1/GFSArtemisia(0)/m/sl' in size <10.95> not a
vailable
(Font) Font shape `EU1/GFSArtemisia(0)/m/it' tried instead on inpu
t line 122.
However, there is no errors when I simply use label=(\alph*) option.

\textdexiakeraiaonly inenumeratelabels or from all counter representations using\alph? – egreg Feb 10 '16 at 09:46babel, you perhaps are using Polyglossia. – egreg Feb 10 '16 at 09:50\textdexiakeraiaonly in thatenumerateenvironment – Yorgos Feb 10 '16 at 09:51textdexiakeraiaoption. However, It doesn't work in my case. – Yorgos Feb 10 '16 at 09:52enumitem-package (at least not in you MWE). – Sveinung Feb 10 '16 at 10:28textdexiakeraia-command is not defined. Perhaps it is something wrong with the font definition? Not defined infontspec? The answer Alananno is referring to in second comment, is using pdflatex, not xelatex. – Sveinung Feb 10 '16 at 10:31textdexiakeraiais not defined when you are using xelatex, fontspec and polyglossia. – Sveinung Feb 10 '16 at 10:38