I am a polyglot - I speak English, Urdu and Hindi and have set these languages as a preference under "Languages" settings. Unfortunately, the default fonts for Urdu and Hindi are not legible enough on Windows. The font settings, ironically, are available for customization for default browser language. I request Edge team to move all font customization options under individual language settings so that custom fonts could be set individually for selected languages. This would definitely improve the experience for those who browse the non-English web.
I just tried it now Version, 78.0.268.0 (Official build) canary (64-bit)
I set Edge display language to something else that is even RTL like Persian or Hebrew and restarted browser. then i went to the appearance settings and changed the fonts, scaling and everything for it and they were all taking effect. it's Different from system language. my system language in Windows is English obviously but Edge only let me change the Edge's language, it's totally disconnected from system language.
My bad for the typo. I meant to say that we can only customize the fonts for the browser under Appearance / Customize fonts settings which does not cover the cases for languages like Urdu or Hindi which are set as subsequently preferred languages under Languages settings. Customization of fonts should cover such preferences as well because most often than not the default fonts for non-latin languages are not legible enough.