Problem with GFS + enumeration

Question

I am trying to nest two enumerate environments, the second inside the first. I am using the xgreek package, which generates the second enumeration as (α'), (β'), (γ') etc. However, when using 2 of the GFS fonts (Elpis & Heraklit), I am facing issues with the ' in the enumeration.

Because I have over 50 .tex files with the nested enumerations, I would prefer to do it with an automatic way and not to have to add a label to every nested enumeration as described on this post.

MWE:

\documentclass[12pt]{article}

\usepackage{enumerate, enumitem, moreenum}
\usepackage{multicol}
\usepackage{fontspec,xgreek, polyglossia}
\defaultfontfeatures{Mapping=tex-text}
\setmainfont[Mapping=tex-text]{CMU Serif} 
\setdefaultlanguage{english}
\newfontfamily\myfontfirst{GFS Elpis}
\newfontfamily\myfontsecond{GFS Artemisia}
\newfontfamily\myfontthird{GFS Heraklit}

\begin{document} 
    
    \begin{multicols}{2}
    CMU Serif
    \begin{enumerate}
        \item 
        \begin{enumerate}
            \item 
            \item 
            \item
            \item 
            \item 
            \item 
        \end{enumerate}
        \item
    \end{enumerate}
    
    {\myfontfirst 
        GFS Elpis
        \begin{enumerate}
            \item 
                \begin{enumerate}
                    \item 
                    \item 
                    \item
                    \item 
                    \item 
                    \item 
                \end{enumerate}
            \item
        \end{enumerate}
    }
    \end{multicols}

    \begin{multicols}{2}
    {\myfontsecond 
        GFS Artemisia
        \begin{enumerate}
            \item 
            \begin{enumerate}
                \item 
                \item 
                \item
                \item 
                \item 
                \item 
            \end{enumerate}
            \item
        \end{enumerate}
    }
    
    {\myfontthird
        GFS Heraklit
        \begin{enumerate}
            \item 
            \begin{enumerate}
                \item 
                \item 
                \item
                \item 
                \item 
                \item 
            \end{enumerate}
            \item
        \end{enumerate}
    }   
    \end{multicols}
    
\end{document}

Answer 1

The fonts GFS Elpis and GFS Heraklit don't have a glyph for U+0374 GREEK NUMERAL SIGN and, indeed, you get

Missing character: There is no ʹ in font GFS Elpis/OT:script=latn;language=dflt;!
Missing character: There is no ʹ in font GFS Heraklit-Regular/OT:script=latn;language=dflt;!

for each item in the second level enumerations when those fonts are in use.

You can provide a fallback using a font that has the glyph, in the code below I adopted GFS Artemisia.

\documentclass[12pt]{article}

\usepackage{fontspec}
\usepackage{xgreek}
\usepackage{enumitem,moreenum}
\usepackage{multicol}

\setmainfont{CMU Serif} 
\newfontfamily\myfontfirst{GFS Elpis}
\newfontfamily\myfontsecond{GFS Artemisia}
\newfontfamily\myfontthird{GFS Heraklit}

\makeatletter
%%% avoid so many spurious warnings
\protected\def\anw@false{\protected\def\anw@print{}}
\protected\def\anw@true{\protected\def\anw@print{\numer@lsign}}
%%% provide a fall back for U+0374 GREEK NUMERAL SIGN
\protected\def\numer@lsign{\iffontchar\font`ʹ ʹ\else{\myfontsecond ʹ}\fi}
\makeatother

\begin{document} 
    
    \begin{multicols}{2}
    CMU Serif
    \begin{enumerate}
        \item 
        \begin{enumerate}
            \item 
            \item 
            \item
            \item 
            \item 
            \item 
        \end{enumerate}
        \item
    \end{enumerate}
    
    {\myfontfirst 
        GFS Elpis
        \begin{enumerate}
            \item 
                \begin{enumerate}
                    \item 
                    \item 
                    \item
                    \item 
                    \item 
                    \item 
                \end{enumerate}
            \item
        \end{enumerate}
    }
    \end{multicols}

    \begin{multicols}{2}
    {\myfontsecond 
        GFS Artemisia
        \begin{enumerate}
            \item 
            \begin{enumerate}
                \item 
                \item 
                \item
                \item 
                \item 
                \item 
            \end{enumerate}
            \item
        \end{enumerate}
    }
    
    {\myfontthird
        GFS Heraklit
        \begin{enumerate}
            \item 
            \begin{enumerate}
                \item 
                \item 
                \item
                \item 
                \item 
                \item 
            \end{enumerate}
            \item
        \end{enumerate}
    }   
    \end{multicols}
    
\end{document}

By the way, don't load enumerate and enumitem together, as they fight each other. Load only the latter.