Insert an english chapter in a document written in arabic

Question

I want to insert in the end of a book, written in arabic using the polyglossia package, a chapter written in english. I try to do this, using the \selectlanguage{english} command, provided by this package, but its compilation with xelatex gives the following error:

! Undefined control sequence. <argument> \MakeUppercase {\ifnum \c@secnumdepth >\m@ne \if@mainmatter \@cha...

How can I do my purpose?

I give the .tex file , producing this error message:

\documentclass[12pt]{book}

\usepackage{polyglossia}

\setdefaultlanguage{arabic}
\setotherlanguage{english}

\setmainfont{Times New Roman}   %% Choose any font
\newfontfamily\englishfont{Times New Roman}

\begin{document}

\selectlanguage{english}
\chapter{An english chapter}

\end{document}

Answer 1

That's obviously a bug in gloss-arabic.ldf. It "reverts" \MakeUppercase to an undefined command.

\documentclass[12pt]{book}
\makeatletter 
 \let\orig@MakeUppercase\MakeUppercase
\makeatother 
\usepackage{polyglossia}

\setdefaultlanguage{arabic}
\setotherlanguage{english}

\setmainfont{Times New Roman}   %% Choose any font
\newfontfamily\englishfont{Times New Roman}

\begin{document}
\selectlanguage{english}
\chapter{An english chapter}

\end{document}