Switching languages in bibliography with biblatex (completely!)

Question

This is a take on this. In the print,

In : LE JOUR (AAAA)

should be

Dans : LE JOUR (AAAA).

Is it feasible, how?

\documentclass{scrbook}

\usepackage[french]{babel}
\usepackage[bibencoding=auto,backend=biber,babel=other]{biblatex}
\usepackage{csquotes}
\usepackage{filecontents}

%\addbibresource{foo.bib}% Syntax for version >= 1.2
\begin{filecontents*}{foo.bib}
@article{bar
  ,author =       "AUTHOR"
  ,title =        "TITLE"
  ,journal =      "JOUR"
  ,year =         "YYYY"
}

@article{lebar
  ,author =       "AUTEUR"
  ,title =        "TITRE"
  ,journal =      "LE JOUR"
  ,year =         "AAAA"
  ,language={french}
  ,hyphenation={french}
}
\end{filecontents*}


\begin{document}

A bare citation command: \autocite{bar}.

A citation command for use in the flow of text: As \textcite{bar} said \dots

Une citation: \autocite{lebar}.

Une citation au milieu du texte: Comme \textcite{lebar} a dit \dots


\printbibliography

\end{document}

Answer 1

Both entries are actually completely in French - at least to the extent controlled by biblatex.

A short look at french.lbx (l. 413, in biblatex 3.13a) shows that biblatex translates "in" into French as "in". If you want "dans" instead, you just need to tell biblatex about that.

Note that at least in the specific constellation of your MWE the autolang option and the langid (formerly hyphenation) field have no influence on the output. biblatex already prints the entries in French since it adapts to the main language of the document, which is French.

\documentclass{article}
\usepackage[french]{babel}
\usepackage{csquotes}
\usepackage[backend=biber,autolang=other]{biblatex}

\DefineBibliographyStrings{french}{
  in = {dans},
}

\usepackage{filecontents}
\begin{filecontents*}{\jobname.bib}
@article{bar
  ,author =       "AUTHOR"
  ,title =        "TITLE"
  ,journal =      "JOUR"
  ,year =         "YYYY"
}
@article{lebar
  ,author =       "AUTEUR"
  ,title =        "TITRE"
  ,journal =      "LE JOUR"
  ,year =         "AAAA"
  ,language={french}
  ,hyphenation={french}
}
\end{filecontents*}
\addbibresource{\jobname.bib}


\begin{document}
A bare citation command: \autocite{bar}.

A citation command for use in the flow of text: As \textcite{bar} said \dots

Une citation: \autocite{lebar}.

Une citation au milieu du texte: Comme \textcite{lebar} a dit \dots

\printbibliography
\end{document}