Suso himself (not merely "a fourteenth-century writer") says that the angels sang him the song; the mention is in his Das Büchlein der ewigen Weisheit, first published in 1328, and since he mentions it as a song already in existence and which may be familiar to his readers, it is clear that it was already extant in that year and quite probably earlier.

As for the Esperanto gibberish (not a redundancy here), it's a mystery to me. I know what went wrong â€" I copy/pasted from my hymnal into the window here, when I should have redone the &#...; parts. What mystifies me is that my version and Father Kronenberger's are differently mispresented. I would have sworn I used the same encoding for both. UTF-8 to be specific. If you set your browser's encoding to "UTF-8 and Auto-Detect Universal" (firefox) or "Unicode (UTF-8)" (IE) the first (my) version should be okay, but the second (Kronenberger's) still has funny little symbols added (although the Esperanto letters are okay; the anomalies are something punctuative). I'll repost them. Sorry for the fuŝo.

Haruo