Tau Cetan n.

‘It is suicide.’ ‘I know.’ ‘Better death,’ the thoughts of the Tau Cetian broke in sharply, ‘than to face the ignominy of retreat.’ ‘I will go with you.’ ‘We knew it, biped. Let us start.’

Not that the Tau Cetian was unprepossessing. He had a certain elfin quality, big dome of a head and small torso poised on four spidery legs, two slender arms waving in time with his fronded ears, hairless pale-gold skin, the face quasi-human but with great green eyes, the clothing a filmy shimmer of veils. His size, below one meter, added to the charm. However, he talked.

Suppose that there are planets of Tau Ceti, and Project Ozma’s beamed radio signals are quite futile—just as futile as the Tau Cetans beamed clairvoyance-band transmissions. Never having worked with the electromagnetic spectrum, they don't have the radio-optical gadget we know as TV; they use an equally sophisticated gadget that is a clairvoyance machine.

The being—the Tau Cetan!—talked so pragmatically, so sensibly, that he provided an anchor to which Burton could tie his senses before they drifted away again. And, despite the repulsive alienness of the creature, he exuded a friendliness and an openness that warmed Burton. Moreover, any creature that came from a civilization which could span many trillions of miles of interstellar space must have very valuable knowledge and resources.

‘Watson, you see, but you do not—oh, forget it. Indeed it is a bottle, Watson; a bottle that once held Chateau Ganymede ’86, fermented from subsurface fungi on Jupiter’s moon, a vile concoction. I keep mine in a radioactive-ash-scuttle. There is your murderer.’ ‘You mean Bruce Dee was drunk.’ ‘As the proverbial Tau Cetan, Watson.’

He peered around the corner, looking for the tall jade-green Tau Cetian: all he saw were the smiling faces of Thais and Indians going about their endless daily business. Reassured, but still wary enough to keep his program enabled, he moved off down the alley.

Writers have used many techniques: [...] Aliens with great language skills, who have mastered English so that the human characters (and readers) don’t have to learn, say, Tau Cetian.

Even after the universal translator is temporarily fixed, Detmer mentions that her control panel is still in ‘tau cetian.’ This seems to reference a language indigenous to the Tau Ceti star system.