To speak of an insanely gorgeous book about frogs would seem to pose a contradiction in terms. To note two such books just seems silly. Yet here they are: “Frog Song,” the latest from Brenda Z. Guiberson and Gennady Spirin (“Life in the Boreal Forest”), and “999 Frogs Wake Up,” a sequel of sorts to 2011’s “999 Tadpoles,” by the Japanese team of Ken Kimura and Yasunari Murakami. Both are about frogs, and both are spectacularly illustrated. There the similarities end.