Empty Speech

The Muli'hes are a twisted mirror image of our appearance, so it is only natural that their language is nothing more than a hollow reflection of our speech, devoid of meaning, emotions, and sound.
~ Lacalan Meraxis, Vein Warden

Also known as Null or Mirror Speech, the Empty Speech is the "mother tongue" of the aberrant genetic abominations known as the Muli'he. Given the eldritch nature of its speakers, it is no wonder that the Empty Speech differs quite drastically from any other known type of language.
Composed of deafening voids that swallow all sounds around them, the Empty Speech is as much a language as it is one of the Muli'hes most dreadful weapons, as it completely conceals their acoustic presence and drowns out the terrified screams of their unfortunates victims.

Writing System

It is not just a claw mark on a mirror. It is a testament to the sins of your vein-line and the very reason as to why I am able to wield as much power as I do.
~ Lacalan Meraxis, Vein Warden

While there have been numerous reports of the Muli'he utilizing a wide assortment of crudely carved symbols to mark certain areas, the exact meaning of these "Mirror Scratches" has so far remained elusive. While some Vein Wardens assume them to be a written version of the Empty Speech, others argue that they are nothing but asemic writing that can't be interpreted in any meaningful way by anyone by the warped minds of the Muli'he.
The only concrete piece of knowledge that exists about the Mirror Scratches, is the fact that they can't be read in any conventional way and instead required a prospective reader to possess the ability of "Mirrorsight" in order to properly read them.
Given that this ability is only available to certain strains of Miwa and the Muli'he themselves, this further complicates research into the Scratches meaning, especially as the Miwa's Mirrorsight is incredibly weak and limited when compared to that of the Muli'he.

Phonetics

Silence in the shape of a word.

The perhaps strangest and also characteristic feature of the Muli'hes speech is the fact that their language is not composed of various sounds and tones. Instead, it appears to be made up entirely of so-called "Null Sounds", which act as the complete antithesis to any kind of vocal communication and therefore actively dampen sounds around them whenever they are spoken.
Because of this, it is almost impossible to understand the Muli'he as their voice can only be "heard" when it is negatively contrasted against a homogeneous soundscape. And even in such an optimal condition, the ears of most species would be simply not sensitive enough to filter out the exact tones that have been swallowed by the Muli'hes voice.
Due to this, only the At-Korvian and certain members of the Haeblash Cult that specialize in the creation of acoustic fashion, have ever been able to properly listen to the voices of a Muli'he.
Given that the Vitreous Empire is not on the best terms with these factions the findings gathered during these "conversations" remain inaccessible to the Empire's Warden of the Veins.

Words from the Void

While it might be impossible to ever fully decipher the language of the Muli'he, the Empire's Vein Wardens were nevertheless able to discern several different "Phrases of Silence" within the Muli'hes soundless speech.
These so-called "Null Sentences" are currently divided into several different categories based on their utilization by the Muli'he and their suspected meaning.

Hunting Screams

The most common Null Sentence utilized by the Muli'he the so-called "Hunting Screams" are extreme "loud" vocalizations that created a bubble of deafening silence around a Muli'he and their victims.
Depending on the number of Muli'he and how strong-voiced they are these bubbles of complete silence can reach several dozen meters in diameters, with the bubble observed during the "Night of Silence" being estimated to have reached a size of more than six kilometers.

Silent Laughter

The "Silent Laughter" is assumed to be the Muli'hes analog to laughter and can most often be heard once the have managed to corner one of their victims.
The few individuals that "heard" this sound and lived to tell their tales, describe it as a feeling of "cyclic deafness that outright oozes malicious delight".

Ticking Hush

The most recent addition to the Muli'hes vocal catalog, the "Ticking Husk" consists of periodic up and down-swelling null sound.
It appears to be a direct counter-measure to the acoustic clickers utilized by the Vein Wardens to detect the usage of Empty Speech in their surroundings, as the pauses in the Husk's rhythmic sounds are perfectly synchronized with the clickers noises, which means that they don't disrupt them like other types of Null Sentences.

Null Song

Trust me you do not want to know what they use these ones for.