What is the ancient language that Leto II and Ghanima use when speaking privately?

Question

In Children of Dune Leto II and Ghanima sometimes use an "ancient language" to converse with each other, a language that only they know of:

Leto reverted to the ancient language they used for privacy: "L'ii ani howr samis sm'kwi owr samit sut."

That was where the decision lodged itself in their awareness. Literally: We will accompany each other into deathliness, though only one may return to report it.

The Golden Path is also referred to as "Secher Nbiw" in this ancient language:

[…] words uttered in the ancient language shared only by the two of them in all this universe. Secher Nbiw. If she heard those words: Golden Path […]

In this reddit thread a user claims that it's a attempt to represent Ancient Egyptian, and there's mention of a Wikipedia article that 'confirms' it but that must have been deleted or moved because I can't find it anywhere.

The Dune Wiki also says it's Ancient Egyptian but provides no sources:

The Golden Path ("Secher Nbiw" in the ancient Egyptian language)…

Is the reddit thread and the Wiki correct? Is there anything (textual clues from the novels, notes from Frank Herbert) that proves the language is indeed Ancient Egyptian? And if not, what exactly is this ancient language?

Answer 1

Leto and Ghanima are speaking to each other in Middle Egyptian. As far as clues in the text are concerned, the major indicator is that Leto keeps waffling on about the Pharoahs, but there's no direct confirmation given.

Out-of-universe, Herbert gives us an English translation for each of the phrases, making it fairly straightforward to see that at least some of the words have been translated directly from whatever Middle Egyptian dictionary he had to hand. All definitions in the following paragraphs are from Ancient Egyptian Dictionary provided by the Ancient Egypt and Archaeology website.

L'ii ani howr samis sm'kwi owr samit sut = "We will accompany each other into deathliness, though only one may return to report it" = sMs = accompany (or rather follow) / ii = return / smi = to report.

Mohw'pwium d'mi hish pash moh'm ka = "The capture of my soul is the capture of a thousand souls." mH = to seize / Ka = soul (or spirit).

m'smow = "The foul smell of a summer night" = smw = summer.

Muriyat = "It must be done lovingly" = mRi = love/loving.

Wabun 'k wabunat = "Rising, thou risest" = wbn = rise, etc.

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Secher Nbiw ("Golden Path") is worthy of our special attention. We can use Raymond Faulkner's A Concise Dictionary of Middle Egyptian to translate it in its entirety. He actually has this as Sch (golden) Nbw = plan (or possible counsel), rather than path.

Answer 2

Yes, there is a textual clue this is some sort of ancient Egyptian language. In Children of Dune, all of this is within a page of each other:

Still in the private language, he said: "It requires the most fortuitous beginning."

They are speaking their private language.

"You are not Osiris." Ghanima reminded him.

A reference to an ancient Egyptian deity. A clue, but not proof.

She had mixed the ancient tongue with Fremen superstition to call up a most basic tribal omen. M'smow, the foul odor of a summer night, was the harbinger of death at the hands of demons. And Isis had been the demon-goddess of death to the people whose tongue they now spoke.

Isis is an ancient Egyptian deity. This confirms the language.

Answer 3

From Children of Dune:

Ghanima took his arm to stop him. “Alia darsatay haunus m’smow,” she warned. Leto stared into his sister’s eyes. Indeed, Alia’s actions did give off a foul smell which their grandmother must have noted. He smiled appreciatively at Ghanima. She had mixed the ancient tongue with Fremen superstition to call up a most basic tribal omen. M’smow, the foul odor of a summer night, was the harbinger of death at the hands of demons. And Isis had been the demon-goddess of death to the people whose tongue they now spoke.

Note - Isis is an Egyptian goddess.