XeTeX: problem with g-brief2 and polyglossia

Question

Today I discovered a problem with the polyglossia package and the g-brief2 class. I hope someone can help me to fix it. :)

Here is my polyglossia MWE (polyg.tex):

\documentclass[a4paper,11pt]{g-brief2}
\usepackage
{%%
    fontspec,
    polyglossia,
    lmodern,
    relsize
}
\setmainlanguage[spelling=new,babelshorthands=true]{german}

\Name               {My Name}
\Unterschrift       {My Name}
\Betreff            {Subject}
\Datum              {\today}
\Anrede             {Dear,}
\Gruss              {Regards,}{0.5cm}

\begin{document}
    \begin{g-brief}
        bla bla bla
    \end{g-brief}
\end{document}

The log for compiling (xelatex polyg.tex) contains the following message:

! Missing control sequence inserted.
<inserted text> 
                \inaccessible 
l.18 ^^I\begin{document}

So, where is the problem? – Best regards and thanks for your assistance!

Answer 1

With TeX Live 2013 I get no error, but, of course, loading both babel and polyglossia can raise some conflicts.

If you avoid loading babel, you get around the error also with older TeX distributions:

%%% Fool LaTeX to have already loaded babel
\makeatletter
\@namedef{[email protected]}{2001/03/01}
\@namedef{[email protected]}{\sprache}
\makeatother
%%% End of trick

\documentclass[a4paper,11pt]{g-brief2}
\usepackage
{%%
    fontspec,
    polyglossia,
    relsize
}
\setmainlanguage[spelling=new,babelshorthands=true]{german}

\Name               {My Name}
\Unterschrift       {My Name}
\Betreff            {Subject}
\Datum              {\today}
\Anrede             {Dear,}
\Gruss              {Regards,}{0.5cm}

\begin{document}
    \begin{g-brief}
        bla bla bla
    \end{g-brief}
\end{document}

Ask the maintainer of g-brief2 an option for avoiding babel.