Default hyphenation / langid field in biblatex

Question

I want to include a lot of bibliography entries in various languages. The great majority are in english and only a handful is in another language. I have no language, langid or hyphenation fields, to use different language per entry. I can manualy add the langid filed to the non-english entries. Is there a way to set langid={english} by default for every entry that it is not set?

Answer 1

The description of the autolang option on p. 48 of the biblatex documentation says

[The autolang] option controls which babel language environment is used if the babel/polyglossia package is loaded and a bibliography entry includes a langid field (see § 2.2.3). Note that Biblatex automatically adjusts to the main document language if babel/polyglossia is loaded. In multilingual documents, it will also continually adjust to the current language as far as citations and the default language of the bibliography is concerned. This option is for switching languages on a per-entry basis within the bibliography.

So if no langid field is provided biblatex falls back to the current language. Consider the following MWE where british is the document language and uthor does not come with a langid field, while torin has ngerman.

\documentclass[ngerman,british]{article}
\usepackage{babel}
\usepackage{csquotes}
\usepackage[style=authoryear-icomp,autolang=other]{biblatex}

\usepackage{filecontents}
\begin{filecontents}{\jobname.bib}
@incollection{uthor,
  author    = {Anne Uthor},
  year      = {2001},
  title     = {An English Title},
  booktitle = {Collection},
  editor    = {Eddie Tor},
}
@incollection{torin,
  author     = {Anne U. Torin},
  year       = {2002},
  title      = {Ein deutscher Titel},
  booktitle  = {Sammelband},
  editor     = {Heinz E. Rausgeber},
  langid     = {ngerman},
}
\end{filecontents}
\addbibresource{\jobname.bib}
\nocite{*}

\begin{document}
\printbibliography
\end{document}

torin is set in German, while uthor remains in (British) English.

---

If you insist on setting the langid field for entries that do not yet have it, use

\DeclareSourcemap{
  \maps[datatype=bibtex]{
    \map{
      \step[fieldset=langid, fieldvalue={english}]
    }
  }
}

since this mapping does not overwrite fields, only those entries without a langid get english now.