Hello and sorry for the late response,
gnome-abrt got its header fixed (through cli client), so plural forms and translation are good there.
currently, the only other* project which I've found need fixing is anaconda (only for consistency, the dual form in all strings is exactly the same as the plural form, and should be),
but I haven't been able to fix its header because it has multiple documents in each branch (and they're overriding each other).
I haven't yet found other translated** projects making use of plural forms.. but I'll keep searching.
Many thanks,
Niv