\listfiles
\documentclass{article}
\usepackage{ifpdf}
\usepackage[frenchb]{babel}
\ifpdf
  \PassOptionsToPackage{german,french}{backref}
  \usepackage[backref]{hyperref}
\else
  \usepackage[dvips,backref]{hyperref}
\fi

\renewcommand*{\backref}[1]{}
\renewcommand*{\backrefalt}[4]{%
  \ifcase #1 %
    No citations.%
  \or
    One citation in section #2.%
  \else
    #1 citations in sections #2.%
  \fi
}

\begin{document}
\section{Hello World}\label{sec:foo}
See \ref{sec:foo}.
\cite{bib:foo}, \cite{bib:foo}

\begin{equation}
v=s/t
\end{equation}

\cite{bib:foo}

\tracingmacros=1
See \cite{bib:abc}.

\newpage
\section{Foo}
\section{Bar}
See again \cite{bib:abc}.

%\show\backrefxxx
\makeatletter
%\show\if@safe@actives
\makeatother
\newcommand*{\backrefxxxdupe}[3]{#2}
\leavevmode
\begin{thebibliography}{9}
\bibitem{bib:abc} First entry.

\bibitem{bib:foo} Second entry.

\end{thebibliography}

\begingroup
  \makeatletter
  \def\x#1{%
    \begingroup
      \csname @safe@activestrue\endcsname
      \expandafter\let\expandafter\a\csname #1@bib:\y\endcsname
      \typeout{* [#1/y] %
        \ifx\a\relax
          <empty>%
        \else
          \expandafter\strip@prefix\meaning\a
        \fi
      }%
    \endgroup
  }%
  \def\y{abc}
  \x{br}
  \x{brc}
  \x{brl}
  \x{brcd}
  \x{brld}
  \def\y{foo}
  \x{br}
  \x{brc}
  \x{brl}
  \x{brcd}
  \x{brld}
\endgroup
\end{document}
