Text scale mode and additional fonts

[Rahguzar <rahguzar@zohomail.eu>]

Hi,
I sometimes write documents with a mix of Urdu and English. For Urdu I
have this in my config:

(setq +bidi-arabic-font (font-spec :family "Mehr Nastaliq Web"))

(set-fontset-font t 'arabic +bidi-arabic-font)

The font can be found here
https://mehrtype.com/product/mehr-nastaliq-web/

This works but Urdu text is too small. I can use `text-scale-increase`
but that also makes the English text bigger. So I tried this snippet
instead:

(setq +bidi-arabic-font (font-spec :family "Mehr Nastaliq Web" :size 28))

(set-fontset-font t 'arabic +bidi-arabic-font)

this makes the initial situation better but now the Urdu text is not
affected by the `text-scale-mode` commands.

To overcome this I have added a hook to `text-scale-mode-hook` to
manually adjust the font size. This improves the situation but feels
wrong since the `text-scale-mode` uses face remapping machinery which is
buffer local but the font sizes are global.

Is there a way to set a different size for my Urdu font that makes it
work seamlessly with `text-scale-mode`?

Thanks,
Rahguzar