Biblatex / Biber with babel ngerman - sentence case not working

Question

When I use biblatex with \usepackage[ngerman]{babel} sentence casing in the references stop working. When I deactivate \usepackage[ngerman]{babel} it works well. See the following MWE:

\documentclass{book}
\usepackage[ngerman]{babel}

\usepackage[backend=biber,natbib=true,style=apa,isbn=false,doi=false,eprint=false,uniquename=false]{biblatex}

\begin{filecontents}{test.bib}
    @article{Bandura.1999,
        author = {Bandura, Albert},
        year = {1999},
        title = {Moral Disengagement in the Perpetration of Inhumanities},
        pages = {193--209},
        volume = {3},
        number = {3},
        issn = {1088-8683},
        journal = {Personality and Social Psychology Review},
        doi = {10.1207/s15327957pspr0303{\textunderscore }3}
    }
\end{filecontents}

\addbibresource{test.bib}

\begin{document}
    \citep{Bandura.1999}
    \printbibliography
\end{document}

How can I combine both (sentence casing for english sources and using ngerman), since the thesis is written in German, but has a lot of English sources.

Answer 1

If you do not explicitly give the language of the entry in the .bib file via the langid field, biblatex will automatically use the rules of the surrounding language. In your case that means that biblatex will not apply sentence casing since sentence casing is not enabled for German (as ordered with ngerman) by default (and it would not make sense to enable it).

The solution is to add langid = {english}, to English works. On the other hand you will also want to add langid = {ngerman}, to the German works you cite in case you want to use them in an English document to avoid sentence casing.

\documentclass{article}
\usepackage[ngerman]{babel}

\usepackage[backend=biber, style=apa]{biblatex}

\begin{filecontents}{\jobname.bib}
@article{Bandura.1999,
  author  = {Bandura, Albert},
  year    = {1999},
  title   = {Moral Disengagement in the Perpetration of Inhumanities},
  pages   = {193--209},
  volume  = {3},
  number  = {3},
  issn    = {1088-8683},
  journal = {Personality and Social Psychology Review},
  doi     = {10.1207/s15327957pspr0303_3},
  langid  = {english},
}
\end{filecontents}
\addbibresource{\jobname.bib}

\begin{document}
  \autocite{Bandura.1999}
  \printbibliography
\end{document}