%%
%% The LaTeX Companion, 3ed
%%
%% Example 16-7-33 on page II-561 in "Sentence casing".
%%
%% Copyright (C) 2022 Frank Mittelbach
%%
%% It may be distributed and/or modified under the conditions
%% of the LaTeX Project Public License, either version 1.3c
%% of this license or (at your option) any later version.
%%
%% See https://www.latex-project.org/lppl.txt for details.
%%

\documentclass{tlc3exa}
\pagestyle{empty}
\setcounter{page}{6}
\setlength\textwidth{159.0pt}
%
  % Use biber program
  \setlength\parindent{0pt}

%StartShownPreambleCommands
\usepackage[ngerman,english]{babel}
\usepackage[style=authortitle]{biblatex}
\addbibresource{tlc.bib}
\DeclareFieldFormat[inproceedings]{citetitle}
   {\mkbibemph{\MakeSentenceCase*{#1}}}
%StopShownPreambleCommands

\begin{document}
\ldots\ \textcite{Southall} \ldots\\[3pt]
But when we switch to German, the citation changes
and is no longer altered:\\[3pt]
\selectlanguage{ngerman}\ldots\ \textcite{Southall}
\end{document}
