What's not to like about it? Even the title has two old timey words: "Hark" and "herald."
"Hark" is of course an imperative mood form of the verb "to hearken," to listen. The Germans preserve this word in their verb horchen, to listen, (not to be confused with their word hören which mean to hear).
"Herald" is fuzzier. The old meaning is "messenger." In the song title, "herald" is an adjective modifying angels. So, a modern translation of the song title might be: "Listen! The Messenger Angels Sing"
But the Anglo-Saxon roots of this song are even deeper than I suspected. First of all, the song is old -- first dating from 1739. According to Wiki, the original first couplet was "Hark how all the Welkin rings." "Welkin" is an archaic English word meaning heavens (lit. clouds). German/Dutch speakers may recognize their modern cognate words Wolke/welk. The lyrics evolved in the 18th and 19th centuries to what we have now.
There are richer, even deeper linguistic connections to the past in that song's lyrics, if you care to dig there.