(Other answers (A, B) with similar error message do not actually take care of the situation.)
I have memoir document which should contain title both in Bangla and English. But when compiled (using xelatex), I get an error message,
! Argument of \reserved@a has an extra }.
Here is the MWE which causes the error.
\documentclass{memoir}
\usepackage{polyglossia}
\setmainlanguage{english}
\setotherlanguage[numerals=Devanagari]{bengali}
\title{\begin{bengali} বইয়ের টাইটেল\end{bengali}
Book Title}
\begin{document}
\maketitle
\end{document}
If the part \begin{bengali} বইয়ের টাইটেল\end{bengali} is taken out of the file,
the error disappears. So, that line must the culprit here.
As is advised in the questions (or answers) mentioned at the top, I need to protect something. However, I am a little confused what to protect here. I even tried putting \protect around \begin{bengali} বইয়ের টাইটেল\end{bengali}, without any avail. (Just a hunch, not an educated one.)
