Making a logo with Arabic text

Question

I am trying to use this answer https://tex.stackexchange.com/a/75652/134574 with Arabic letters:

I can replace the MTG in the center of the logo (replaced by my command \ism in the preamble with arabic letters), but I can't do it around the circle (I put my attempt in a comment). Here is my working modification:

% !TeX program = xelatex
\documentclass[tikz]{standalone}
\usetikzlibrary{decorations.text}
\usepackage{fontspec,amssymb}
\setmainfont{OptimusPrinceps}
\definecolor{byublue}{RGB}{0 34 85}
\newfontfamily\bolderfont{OptimusPrincepsSemiBold}

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\usepackage{fontspec}
\usepackage{polyglossia}


\setmainlanguage{english}
\setotherlanguage{arabic}
\newfontfamily\arabicfont[Script=Arabic]{DecoType Thuluth II}
%\newfontfamily\arabicfont[Script=Arabic]{Scheherazade}

\newcommand{\ism}{\textarabic{بسم الله الرحمن الرحيم}}
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%


\begin{document}

\begin{tikzpicture}
\begin{scope}
\draw[color=gray,fill=byublue] (0,0) circle (3.5cm);
\draw[color=gray,fill=white] (0,0) circle (2.6cm);
\end{scope}
%\draw[color=gray] (0,0) circle (2.5cm) node[scale=1.5] (m) 
%{\Huge\bolderfont MTG};
\draw[color=gray] (0,0) circle (2.5cm) node[scale=1.5] (m) 
{\large\bolderfont \ism};



\draw[color=gray] (0,0) circle (3.6cm);
\path [postaction={decorate,decoration={raise=-1ex,text along path, 
reverse path,text align=center, text={|\huge\color{white}|Quick Latin 
Motto Erratum Et Al.}}}] (-30:3.05cm) arc (-30:210:3.05cm);
\node[white,rotate=-60] at (210:3.05cm) {$\blacklozenge$};
\node[white,rotate=60] at (330:3.05cm) {$\blacklozenge$};

\path [postaction={decorate,decoration={raise=-1ex,text along path, text 
align=center, text={|\huge\color{white}|St. John's College }}}] 
(210:3.05cm) arc (210:330:3.05cm);

 %%%%%%%%\path [postaction={decorate,decoration={raise=-1ex,text along 
 %%%path, text align=center, text={|\huge\color{white}| \ism }}}] 
 %%(210:3.05cm) arc (210:330:3.05cm);


 \end{tikzpicture}

 \end{document}

The fonts I am using can be found here: thuluth fonts.

Here's the output pdf I have:

Answer 1

(Sorry if the text doesn't make any sense, but) here you go:

Your code didn't work because you can't use a macro (\ism) there, only plain text because the command used to make the text circular does not expand macros. And you also have to explicitly tell it to use \arabicfont otherwise it will not find the glyphs it needs.

% !TeX program = xelatex
\documentclass[tikz]{standalone}
\usetikzlibrary{decorations.text}
\usepackage{fontspec,amssymb}
\setmainfont{OptimusPrinceps}
\definecolor{byublue}{RGB}{0 34 85}
\newfontfamily\bolderfont{OptimusPrincepsSemiBold}

%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\usepackage{fontspec}
\usepackage{polyglossia}


\setmainlanguage{english}
\setotherlanguage{arabic}
\newfontfamily\arabicfont[Script=Arabic]{DecoType Thuluth II}
%\newfontfamily\arabicfont[Script=Arabic]{Scheherazade}

\newcommand{\ism}{\textarabic{بسم الله الرحمن الرحيم}}
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

\begin{document}

\begin{tikzpicture}
\begin{scope}
\draw[color=gray,fill=byublue] (0,0) circle (3.5cm);
\draw[color=gray,fill=white] (0,0) circle (2.6cm);
\end{scope}
%\draw[color=gray] (0,0) circle (2.5cm) node[scale=1.5] (m) 
%{\Huge\bolderfont MTG};
\draw[color=gray] (0,0) circle (2.5cm) node[scale=1.5] (m) 
{\large\bolderfont \ism};

\draw[color=gray] (0,0) circle (3.6cm);
\path [postaction={decorate,decoration={raise=-0.5ex,text along path, 
reverse path,text align=center, text={|\LARGE\color{white}\arabicfont|بسم الله الرحمن الرحيم بسم الله الرحم
}}}] (-20:3.05cm) arc (-20:200:3.05cm);
\node[white,rotate=-60] at (200:3.05cm) {$\blacklozenge$};
\node[white,rotate=60] at  (-20:3.05cm) {$\blacklozenge$};

\path [postaction={decorate,decoration={raise=-0.5ex,text along 
path, text align=center, text={|\LARGE\color{white}\arabicfont|بسم الله الرحمن الرحيم
}}}]
(200:3.05cm) arc (200:340:3.05cm);

\end{tikzpicture}

\end{document}