Horrorterror

Horrorterror is the language spoken by the monstruous otherwordly being from Lovecraftian horror, or at the very least an approximate of my devise.

Analysis
Analyzing the language has a fair share of problems on both levels of the analysis; on a meta level the "Language" is most likely random gibberish made to look scary which means trying to make things be consistent is complicated.

On an in-world level we have many more problems, let's take for example the analysis of the most known sentence:

Ph’nglui mglw’nafh Cthulhu R’lyeh wgah’nagl fhtagn.

Even if we assume the narrator of the story is reliable and therefore wrote the sentence in perfect roman transliteration, we can't assume the speaker was reliable. The Great Old Ones are told to have adverse effects on the sanity of those who witness them, and their language sound deeply inhuman and plain wrong when heard by humans - in a clear case of Black speech, although whether that's because of the language or the speakers is not fully known - which means that the interpretation of the language could be wrong by default.

As an example of this, if you say a sentence in !Xoo or even something less esoteric like Chinese, to an English speaker that has zero knowledge of that language and ask him to repeat it he'll probably mangle it beyond recognition. Ask him to read that sentence from a piece of paper will also result in mangling. The only way to make sure there's no mangling is either to use a language that can completely exist within the rules of English (which we can easily see from that sentence, that it doesn't) or to, in the first case, to repeat that sentence until they get it, but given the speaker status that's just plain unfeasible.

Yet another problem arises in the fact that there are a lot of ways to interpret the sentence, giving us no meaningful insight in either phonology or grammar. For example:

 could be /pʰ/ /ph/ /ɸ/ /f/, as well signalizing fortis/lenis distinction among several other things.

<'> could be literally everything, from /h//ħ//ʔ/ to maybe even a vowel like /ə/ to more esoteric things like pharyngealization, ejectivization, the fortis/lenis distinction, a sound that was contracted and lost during speech, a non-pulmonic sound, tone, vocalization of the , vocalization of the following  or  the fact that  is voiced or affricativized, etc.

Which means that while we can grue certain sounds or structures we can't necessarily take anything of these as the gospel truth (unless the speakers are the Great Old Ones).

We do have Word of God on Cthulhu being pronounced somewhat like /qlɤhlu/, although the same source claims the author gave conflicting pronunciations in different occasions.

Consonants
In bold are the sounds we can reasonably expect to be on the language: