[Tex/LaTex] Why can’t sectsty change the chapter font when it’s used with babel package

Question

I'm using Latex to write my thesis in Hungarian, so I include in the preamble the following:

\usepackage[magyar]{babel}

Once this is loaded, I get "Chapter", "Figure", etc. in Hungarian and with matching typography.

I would like to use a sans-serif font in chapter, section and subsection headings. To achieve this, I use the sectsty package, set up like this:

\usepackage{sectsty}
\chapterfont{\usefont{T1}{qhv}{b}{n}\selectfont\huge} 
\sectionfont{\usefont{T1}{qhv}{b}{n}\selectfont\LARGE}
\subsectionfont{\usefont{T1}{qhv}{b}{n}\selectfont\Large}

LaTeX correctly sets sections and subsections in TeX Gyre, but chapter headings stay unchanged, while unnumbered chapters (\chapter*{...})
get changed like they are supposed to.

Example:

while

I suspect the conflict is caused by babel, which redefines the chapter heading in some way sectsty won't be able to handle.

Does anyone have any idea how to manage this? I have tried titlesec, but it behaves in the same way.

Thank you!

Edit:

I created a short document with every relevant package to recreate the problem:

\documentclass[a4paper]{report} 
\usepackage[magyar]{babel}
\usepackage[utf8]{inputenc}
\usepackage{t1enc}

\usepackage{blindtext}

\usepackage{sectsty}
\chapterfont{\usefont{T1}{qhv}{b}{n}\selectfont\huge} 
\sectionfont{\usefont{T1}{qhv}{b}{n}\selectfont\LARGE}
\subsectionfont{\usefont{T1}{qhv}{b}{n}\selectfont\Large}

\begin{document}

    \chapter{Example chapter} %% this one is not working correctly

    \blindtext

    \section{Example section}

    \blindtext

    \subsection{Example subsection}

    \blindtext

    \chapter*{Example unnumbered chapter}

    \blindtext

\end{document}

If I comment out babel, sectsty works as expected but I lose the localization obviously.

Answer 1

The magyar option seizes the initiative and changes the code for \@chapter to reflect the original code in the class and ignores the settings by sectsty. It does nothing to \@schapter, which is the reason you see sans serif in unnumbered chapters.

Use titlesec, instead:

\documentclass[a4paper]{report} 

\usepackage[sf,bf]{titlesec}
\usepackage[T1]{fontenc}
\usepackage[utf8]{inputenc}

\newcommand\magyarOptions{chapterhead=unchanged}
\usepackage[magyar]{babel}

\usepackage{blindtext}

\renewcommand{\sfdefault}{qhv}

\titleformat{\chapter}[display]
  {\sffamily\bfseries\huge}
  {\thechapter. \chaptername}
  {20pt}
  {}

\begin{document}

\chapter{Example chapter} %% this one is not working correctly

\blindtext

\section{Example section}

\blindtext

\subsection{Example subsection}

\blindtext

\chapter*{Example unnumbered chapter}

\blindtext

\end{document}