Why gives biblatex warning when it properly loads Hungarian?

Question

As of biblatex v3.12, it supports the Hungarian language, but I get a warning when I try to run pdflatex.

I have the files mwe.tex:

\UseRawInputEncoding % https://tex.stackexchange.com/a/446653/126797
\documentclass{article}

\usepackage[T1]{fontenc}
\usepackage[utf8]{inputenc}
\usepackage{lmodern}

\usepackage[magyar]{babel}
\usepackage[autostyle]{csquotes}
\DeclareQuoteStyle{magyar}{,,}{''}{>>}{<<} %magyar is not supported
\usepackage{biblatex}
\addbibresource{references.bib}

\begin{document}

Ref: \cite{testsource}.    

\printbibliography
\end{document}

and references.bib:

@article{testsource,
author = {Test Author},
title = {Test title},
journal = {Test Journal}
}

If I run pdflatex mwe, biber mwe, pdflatex mwe and pdflatex mwe, I get the Warning: Package biblatex Warning: Hungarian localisation module for biblatex loaded. Isn't it a bad design to drop a warning even though I did everything to load it correctly? Or did I make a mistake?

The warning message also states that

(biblatex) This warning can be disabled with
(biblatex) '\BiblatexHungarianWarningOff'.

But if I write \BiblatexHungarianWarningOff into the code, I get

! Undefined control sequence. 
<recently read> \BiblatexHungarianWarningOff

How to properly suppress the warning message?

Answer 1

Section 3.16 of the biblatex manual explains, why you get the warning:

The Hungarian localisation module needs to redefine certain field formats to obtain the grammatically correct word order. This means that these field formats are overwritten whenever the Hungarian localisation is active, no matter whether they were defined in the preamble or by a custom style. So please be aware that using the Hungarian localisation module may cause the bibliography output to deviate from the format dictated by the loaded style and preamble definitions. Changes to this behaviour need to be made using \DefineBibliographyExtras. In particular \mkpageprefix is redefined to output the page number as a prefix following Hungarian convention, and all formats of fields involving pages were modified so that page ranges are printed as ordinal ranges. The Hungarian localisation module will print a warning to remind you of these changes whenever it is loaded in a document. The warning tells you how to silence it.

In order to turn the warning off, you have to call \BiblatexHungarianWarningOff after \usepackage{biblatex}

Answer 2

The full warning in the log states the reason for the warning:

Package biblatex Warning: Hungarian localisation module for biblatex loaded.
(biblatex)                This module changes more definitions than usual.
(biblatex)                Please refer to the documentation for hints and
(biblatex)                check the output, especially with non-standard
(biblatex)                styles or customisations to field formats.
(biblatex)                This warning can be disabled with
(biblatex)                '\BiblatexHungarianWarningOff'.

It is, of course, just a warning, not an error. But the extensive changes, and perhaps the fact that this is a somewhat new localization module, presumably motivated developers to leave this warning.

However, \BiblatexHungarianWarningOff is indeed defined in biblatex.sty, and you should thus load it after the call to biblatex:

\UseRawInputEncoding % https://tex.stackexchange.com/a/446653/126797
\documentclass{article}

\usepackage[T1]{fontenc}
\usepackage[utf8]{inputenc}
\usepackage{lmodern}

\usepackage[magyar]{babel}
\usepackage[autostyle]{csquotes}
\DeclareQuoteStyle{magyar}{,,}{''}{>>}{<<} %magyar is not supported
\usepackage{biblatex}
\BiblatexHungarianWarningOff

\addbibresource{references.bib}

\begin{document}

Ref: \cite{testsource}.

\printbibliography
\end{document}