P.S. Isn't it supposed to be a translation from the Elvish? I wonder if the Elvish has a more regular meter to it. I wonder whether Tolkien is actually trying to get the effect of a _translation_ in which an (imaginary) translator took liberties with the meter in order to preserve the meaning.

It certainly isn't any regular "jingly" meter. I think I hear four accented syllable in every line. Since Tolkien was a middle-English scholar and an expert on "Beowulf," I'm guessing that it might have more to do with the verse forms described here-- https://www.wmich.edu/medieval/resources/IOE/pometer.html --then with one of the more regular forms that get names like "iambic pentameter." It sounds just a little bit like the meter of Browning's "How They Brought the Good News from Ghent to Aix:" "I spring to the stirrup, and Joris, and he; I gallop’d, Dirck gallop’d, we gallop’d all three;" which is--which is--oh, never mind, I just Googled and that one is complicated, too.