[Nippom]

I'll tell you one thing I just thought of.
I've been taught that there are no plurals in Nihongo.

Thus, don't you think the poem might better read like this?

Countless are the mountain in Yamato,
But perfect is the heavenly hill of Kagu;
When I climb it and survey my realm,
Over the wide plain the smoke-wreath rise and rise,
Over the wide lake the gull are on the wing;
A beautiful land it is, the land of Yamato!