# Biblatex using polyglossia language setting

I noticed biblatex uses the language option passed to polyglossia first, before acknowledging the option passed to it via the language = <language> option.

Here is the MWE that illustrates the problem.

\documentclass[slovene,a4paper,12pt]{article}
\usepackage{polyglossia}
\usepackage[language=slovene, backend=biber]{biblatex}
\usepackage[autostyle]{csquotes}

\setdefaultlanguage{slovenian}
\DeclareLanguageMapping{slovene}{slovene-apa}

\begin{document}
Cite here \parencite{aksin}.
\printbibliography
\end{document}


The example compiles fine, but how can I avoid the warning given:

Package biblatex Warning: Language 'slovenian' not supported.

(biblatex) Using fallback language 'slovene' on input line 25.

• You can't really avoid this currently as biblatex will always try to automatically detect the language from the default polyglossia/babel language first. This is an annoying artefact due to biblatex and polyglossia naming languages differently. I hope in the future that polyglossia and babel can standardise on BCP47 locale names (biber already supports these and maps internally to the polyglossia/babel names). – PLK May 8 '16 at 13:23
• Thank you for your answer, @PLK. Care to write this as an answer I can accept? I would say it is indeed (a temporary) answer anyhow. – Fato39 May 10 '16 at 18:02
• @Fato39 I tried your MWE and it compiles indeed, but the problem with language naming incompatibility persists. The bibliography strings like andothers or pages still lack translation into Slovene/Slovenian language (sl-SI). PS: What is the \DeclareLanguageMapping for? – Vid Merljak May 24 '17 at 10:23

Consulting with biblatex maintainer Philip Kime, I give you his solution:
\DeclareLanguageMapping{slovenian}{slovene}

makes biblatex and biber understand that both language identifiers refer to the same sl-SI language (see package documentation, as @moewe suggests). Hence the bibliography strings like andothers or pages successfully get their respective translations - which was not the case when I compiled the MWE provided in the question.
Regarding the warnings in the log file, I would confirm that they cannot be avoided. That is, until the slovenian identifier is hard-coded into biblatex as a synonym for slovene, just like UKenglish is for british.
biblatex will always try to automatically detect the language from the default polyglossia/babel language first. The problem you are seeing is an annoying artefact due to biblatex and polyglossia naming languages differently. I hope in the future that polyglossia and babel can standardise on BCP47 locale names (biber already supports these and maps internally to the polyglossia/babel names).