I received some Arabic-language emails written in the Perso–Arabic script. The default fonts severely impede Arabic readability, so I went about changing them. I accessed the fonts configuration via the "Advanced" button in the "Language & Appearance" section. Font settings per writing system (Latin, Arabic, etc.) are ostensibly offered, but I have not observed any such settings take effect after experimenting with the Arabic and Latin settings.

I have managed to only change the fonts globally (i.e. across all scripts) via "Other Writing Systems". Did those per-script font settings become deprecated at some point, or am I interpreting/using it wrong?