Not just aliens but all speakers of imaginary languages. Think about it. A polytheist who says “My god!” means something quite different than does a monotheist—and wouldn’t capitalize.
In Listening at the Gate I needed an epithet for use by Nondany, the itinerant master folklore collector. I settled on “By life!” I like it so much I want to get a slang wave going.
Recently a librarian nailed me with a steel eye and asked whether there was any “bad language” in the novel. I explained that it took place in an imaginary culture, but since all cultures have profanity, I’d had to invent some. She looked baffled. And bought the book.
“If you ask: Why spend time on a writer of escape literature? please consider for a moment the position that the literature of fantasy and science fiction provides more direct functional access to reality than any other modern work of the intellect. When experience is rendered ineffable by a rate of change that undermines the meanings of language, a literature that has evolved to speak out from the middle of the waterfall of ideas can continue to engage and to convey the most important meanings. And this is not a new discovery. The oldest roots and origins of literature, the epics of Gilgamesh and Innana, the Odyssey, the Iliad, all are either fantasy, if you do not believe in the Gods, or science fiction, if you do.”
Margot Adler, Heretic’s Heart: A Journey Through Spirit and Revolution