Cat ‘speaking in tongues’ is the guttural yowl of a cat not to be messed with
This is a really nice example of a ‘cat speaking in tongues’, as Lori Dorn describes it, on the Laughing Squid website. This strange guttural yowl is often seen on the internet and it puzzles a lot of people. It is not the sort of sound you’d expect a domestic cat to make but they can all do it.

Cat speaking in tongues! Actually it’s a guttural yowl to give the impression he is large and dangerous.
It’s a low-pitched sound which tells us the cat’s intention is to give the impression to the receiver of the sound (usually another cat) that he/she is large and not to be messed with. The hostile intruder then slinks away duly frightened off. That’s the way it is meant to work and how the sound is usually deployed.
It might happen when a resident cat meets a stranger cat on the resident cat’s territory. They might square off against each other and start the sumo style pre-fight procedure which includes ‘speaking in tongues’, arching the back, pulling the ears back and flat, fluffing the tail, presenting the body sideways on (to look larger) and erecting the hairs along the spine.
In addition to the yowls there will be spitting, hisses and snarls.
In the video, below, the cat is Chibi Maru who is in Japan (this is a Japanese style feline name). There are three siblings. Chibi Maru has noticed his/her owner (or perhaps a stranger) with a video camera or smartphone filming him and has not taken kindly to it. He seems to have decided that the ‘strange entity’ (his owner) needs to be seen off and commences the guttural yowl. Nice video.
The objective of the pre-fight behavior is to avoid a fight. Both see the other as risky to fight and therefore avoid one. The performance ends with the intruder very slowly (to avoid looking like he is defeated) moving away and disappearing. Job done.