/usr/share/javascript/mathjax/localization/pt/ is in libjs-mathjax 2.6.1-1.
This file is owned by root:root, with mode 0o755.
..
/usr/share/javascript/mathjax/localization/pt-br/FontWarnings.js
/usr/share/javascript/mathjax/localization/pt-br/HTML-CSS.js
/usr/share/javascript/mathjax/localization/pt-br/HelpDialog.js
/usr/share/javascript/mathjax/localization/pt-br/MathML.js
/usr/share/javascript/mathjax/localization/pt-br/MathMenu.js
/usr/share/javascript/mathjax/localization/pt-br/TeX.js
/usr/share/javascript/mathjax/localization/pt-br/pt-br.js
/usr/share/javascript/mathjax/localization/pt/FontWarnings.js
/usr/share/javascript/mathjax/localization/pt/HTML-CSS.js
/usr/share/javascript/mathjax/localization/pt/HelpDialog.js
/usr/share/javascript/mathjax/localization/pt/MathML.js
/usr/share/javascript/mathjax/localization/pt/MathMenu.js
/usr/share/javascript/mathjax/localization/pt/TeX.js
/usr/share/javascript/mathjax/localization/pt/pt.js