Right. As regards the UI variant choice, and since I don’t speak Arabic, I have absolutely no own opinion, but refer solely to the above discussion. As regards monospace, and since Ubuntu has DejaVu Sans Mono, it wouldn’t be so wise IMO to specify a non-monospace font just because they do so in Chrome OS.
(The issue in gnome-terminal meaning that you need to specify the Arabic monospace font manually remains, if I recall it correctly, but for the desktop itself there are other mechanisms but fontconfig to determine fonts, and the issue is probably caused by those.)
Thanks. That font seems to be provided by the texlive-fonts-extra package in Debian/Ubuntu. Installing it would add 2 GB disk space, so it’s not an option for the default configuration.
Mostly because I had the possible next step in mind, i.e. making Noto fonts default for most standard Ubuntu users as it currently is in Kubuntu. In that scenario we would skip the lang test, which would make it necessary to state Noto Sans first (as Chrome OS does, btw).
My interpretation of that Google document is that it applies to CSS properties in documents and applications, which is something else but a system wide default fontconfig configuration if I understand it correctly. And it’s merely an example, isn’t it? They say: " It is recommended to retain "Noto Sans" in the list." And we do so.
But more importantly: Are you aware of a case where switching the order would matter in practice?