Yes, I think this is good enough for "this package needs a default European font" for now.

(A package that requires a specific font to function should specify that explicitly, as you also say next.)

I somewhat disagree with this. Shouldn't it rather depend on langpacks-core-en?

Otherwise we are back to the problem that some random font will be selected.

langpacks-core-en is the provider of font(:lang=en) nowadays (tomorrow i18n may choose to provide it with something else)

One concern on this is what if applications wants a specific generic family. langpacks-core-font-* provides a default sans-serif font so far. if we have those sentence in the guidelines, how does it take care of such case? more likely to see for terminal applications say.

Just to clarify with https://fedoraproject.org/wiki/Changes/FontLangProvidesToLangpacks for F32 we have moved all the previously generated font(:lang=xx) provides from fonts packages into langpacks-core-font-xx.

Personally I think using Requires: langpacks-core-font-en is fine too.
We mainly wanted to keep font(:lang=xx) for compatibility with PackageKit-gtk3-module.

Commit fe80021a fixes this pull-request