Refactored the code.

% the same effect.

%    \begin{macrocode}

\newif\ifthesis@loaded\thesis@loadedfalse

\AtEndPreamble{\thesisload}

\BeforeBeginEnvironment{document}{\thesisload}

\def\thesis@load{\thesisload}

\def\thesisload{%

  \ifthesis@loaded\else

        \RequirePackage[base]{babel}}

    \fi

%    \end{macrocode}

% Consequently, the style files are loaded. If the user specified an

% explicit empty string as the value of |\thesis@style|, do nothing.

%    \begin{macrocode}

      \ifx\thesis@style\empty\else

        \thesis@requireStyle{\thesis@style}

      \fi

%    \end{macrocode}

% If the \textsf{babel} or \textsf{polyglossia} locale is identical

% to the thesis locale, the |\thesis@selectLocale| macro will be

% used to globally set up the \textsf{csquotes} style appropriate for

        \endgroup

      \fi

    \fi

      \fi

%    \end{macrocode}

% Consequently, the style files are loaded. If the user specified an

% explicit empty string as the value of |\thesis@style|, do nothing.

%    \begin{macrocode}

      \ifx\thesis@style\empty\else

        \thesis@requireStyle{\thesis@style}

      \fi

%    \end{macrocode}

% With the placeholder strings loaded from the locale files, we

% can now inject metadata into the resulting PDF file. To this

% locale, \textsf{csquotes}, and hyphenation settings return back to

% what the user has specified after the localized blocks of

% typographic material.

%

% If not loaded by the user, the \textsf{csquotes} package gets

% loaded at the end of the preamble.

%    \begin{macrocode}

\AtEndPreamble{\thesis@require{csquotes}}

\def\thesis@selectLocale#1{%

  \edef\thesis@locale{#1}%

  \ltx@ifpackageloaded{csquotes}{%

    \csq@setstyle{\thesis@@{csquotesStyle}}%

  }{}%

  \ltx@ifpackageloaded{polyglossia}{%

    \selectlanguage{\thesis@locale}

  }{%