Annoying box next to the letter

Question

Ηow can I get rid of this annoying box next to the letter as well the full stop

update-1: but to keep the Greek alphabet to the second level

\documentclass[b5paper,10pt]{book}

\usepackage[cm-default]{fontspec}
\usepackage{xgreek}
\setmainfont{Arial}

\usepackage{enumitem}
\renewcommand{\theenumi}{\roman{enumi})}    


\begin{document}

\begin{enumerate}
 \item text

  \begin{enumerate}
   \item text
  \end{enumerate}

\end{enumerate}

\end{document}

Answer 1

The annoying box is because Greek numerals should be followed by the character that xgreek calls \anwtonos, U+0374 (GREEK NUMERAL SIGN) that's apparently missing in Arial.

You can get redefine \anwtonos to everything you want, even to nothing:

\documentclass[b5paper,10pt]{book}

\usepackage[cm-default]{fontspec}
\usepackage{xgreek}
\setmainfont{Old Standard}

\usepackage{enumitem}
\setlist[enumerate,1]{label=\roman*)}

\renewcommand{\anwtonos}{}

\begin{document}

\begin{enumerate}
 \item text

  \begin{enumerate}
   \item text
  \end{enumerate}

\end{enumerate}

\end{document}

The example uses Old Standard because it's one where U+0374 is present. Use whatever font with Greek characters you prefer.

Answer 2

The "box" means that you are using a char which is not in the font. xgreek prints after the alpha the Unicode Character 'GREEK NUMERAL SIGN' (U+0374) but it is not in Arial.

You should either switch to another font (e.g. Arial Unicode MS) or redefine \greeknumeral, or \anwtonos