Ibis

Oui, j’irai dans l’ombre terreuse.
Ô mort certaine, ainsi soit-il !
Latin mortel, parole affreuse,
Ibis, oiseau des bords du Nil.

Ibis

Ja, ik zal het grondige duister betreden.
O zekere dood, amen, het zij zo !
Dodelijk Latijn, afschuwelijk woord,
Ibis [jij zult gaan], vogel van de oevers van de Nijl.

Ibis

Yes, I will go into the earthly dark.
Oh certain death, so let it be !
Deadly Latin, frightful words,
Ibis [you will go], bird of the banks of the Nile.

Ibis = Bird (Threskiornis aethiopicus; or Sacred African Ibis), a link to Toth, the ibis-headed god of writing and wisdom, who also records the judgement of the dead. This god is already mentioned by Apollinaire in the Orpheus note, where he is identified with 'Hermes Trismegistus'.
Ibis = Latin verb: Futurum 2nd person singular from 'ire' (to go): You will go. . Why not tranlate the entire poem into... Latin?

Ibo in umbram terrosam.
O mors certa, ita fiat!
Lingua Latina letalis, verbum dirum:
Ibis, avis riparum Nili.

In Latin the last line reads in two ways: "Ibis, bird of the Nile" and as "You will go, bird of the Nile". There might also be an echo of the schoolbook oracle: "Ibis redibis nunquam per bella peribis". Ibis (= you will go, and never return), lethal Latin.