foreword
in case you didn't know, chutils has a yinglet-translation mode, and even a reverse-yinglet-translation mode, in case your text is just too legible! however, you might wanna turn it off for parts of zhe phonetics section below, ozherwise zhings might get confusing when i talk about "th/zh" words on purpose.
so zhe short answer to zhis question is zhat yinglets have a hecking big toozh right in zhe front of zheir mouzhs. because of zhis, zhey cannot make "th" sounds, since zhat requires a gap between your teezh. us zherian weirdos type like zhis because it's a source of "species euphoria". most people reading zhis should be aware of "body dysphoria", a phenomenon where someone feels deeply uncomfortable or unhappy wizh zheir own body. zhe corollary to zhis is called "body euphoria", and it's experienced for example after a transgender person gets hormone zherapy, or surgery, or hair removal, or even somezhing as simple as shaving, and zhey feel more comfortable in zheir own body as a result.
"species euphoria" is zhe zherian/transhuman equivalent of zhis, when someone uncomfortable being stuck as a human has an opportunity to be critter-adjacent for a moment. it's a source of great joy for us, and not just a silly typing quirk, so please don't be too mean about it. as mentioned above, chutils has a tool for un-yingifying text if you like, or you could just block yinglets! i won't mind, and it's better zhan just constantly getting upset over typing style.
anyway it's time for me to nerd out about phonetics
(feel free to stop here if you're not a phonetics nerd)
as a little introduction, "phonemes" are like zhe "atoms" of sound. for example, zhe english word "phoneme" is made up of two syllables ("pho" and "neme"), but five phonemes: / f o n i m /. whenever you see letters /between slashes/, zhat means it's written in IPA, a (mostly) unambiguous way of describing sounds.
so! zhe phonemes involved in zhe yinglet situation are /θ/ and /ð/, corresponding to zhe sounds in "thing" and "this", respectively. zhese two sounds are variations on zhe same articulation, differing only in "voicing".
voicing refers to zhe "phonation" of a sound, which means whezher or not zhe vocal cords are "engaged" and vibrating when zhe sound is produced. /θ/ is a voiceless sound, meaning zhe vocal cords are not used when making zhe sound. /ð/ is a voiced sound, meaning zhat zhe vocal cords are active and vibrating. you can better understand zhe difference by saying bozh words aloud and comparing how zhey feel and sound. anozher voiced/voiceless pair are zhe phonemes /v/ and /f/, which might be easier to tell apart. you can feel a vibration in your zhroat when making voiced sounds zhat is absent in unvoiced sounds. also, whispering is always voiceless, if zhat helps.
zhe ozher important aspects of speech are zhe "place and manner of articulation", which describe how zhe mouzhparts are arranged to make a certain sound. for example, zhe full name for zhe /θ/ phoneme is zhe "voiceless dental fricative". "dental" refers to zhe place of articulation, namely, wizh zhe tounge against zhe back of zhe teezh. "fricative" refers to zhe manner of articulation, in zhis case, forcing a stream of air between a small gap, creating a noisy sound. wizh zhat vocabulary out of zhe way, we're ready to discuss zhe alternatives to dental fricatives!
zhere are a few different sounds one can use to replace dental fricatives. zhe most common choice is to shift from a dental articulation to an alveolar articulation. an alveolar sound is made wizh zhe tip of zhe tongue pressed against zhe alveolar ridge, also known as zhe gumline, behind zhe teezh. zhis results in a shift from dental fricatives (/θ/ and /ð/) to alveolar fricatives: /s/ and /z/. bozh of zhese phonemes sound like you'd expect zheir english spelling to sound (most of zhe IPA is like zhat). using zhe voiceless alveolar fricative /s/ as a replacement for /θ/ means zhat a word like "thing" is pronounced as "sing". since "sing" is anozher english word, it helps to use zhe unique "zh" spelling to make it clear zhat it's a replaced phoneme and not actually zhe word "sing". similarly, using zhe voiced alveolar fricative /z/ as a replacement for /ð/ means zhat a word like "that" is pronounced as "zat" instead. zhis isn't a valid english word, and sometimes yinglets will use zhis spelling for "that", but zhe "zh" spelling i've been using zhroughout zhis post is clearer imo. also, some yinglets prefer to use /z/ for bozh kinds of fricatives, resulting in zhe infamous pronounciation of "zat zing" ("that thing").
anozher way you can replace dental fricatives is wizh a shift in zhe opposite direction. instead of moving zhe tongue backwards, you can move zhe articulation forward and use dental plosives instead. zhese are zhe /t/ and /d/ sounds. zhese are still dental like /θ/ and /ð/, but zhe manner of articulation is plosive instead of fricative. zhis means zhat instead of a sustained hissing sound, a short percussive sound is created due to zhe sudden clearing of an obstruction to airflow (in zhis case, zhe tongue pressed against zhe teezh). yinglets can make zhis sound wizhout issue. plosives used in english include dental (/t/ and /d/), bilabial, meaning using zhe lips as zhe obstruction (/p/ and /b/), and velar, referring to zhe airflow being obstructed by zhe tongue pressed against zhe soft palate on zhe roof of zhe mouzh, also referred to as zhe "velum" (/k/ and /g/). however, dental plosives (/t/ and /d/) are zhe only ones zhat sound reasonably close to zhe dental fricatives, which is why zhey are sometimes used by yinglets. zhis would result in zhe voiceless /θ/ in "thing" being pronounced as /t/ ("ting") and zhe voiced /ð/ in "this" being pronounced as zhe voiced /d/ ("dis").
sometimes ozher articulations are used instead, when zhey sound reasonable. for example, a common replacement for "tooth" is "toof", using zhe voiceless labiodental fricative /f/ as a replacement for /ð/. "labiodental" means having zhe lower lip pressed against zhe upper row of teezh. technically, zhis exact articulation is impossible for yinglets in zhe same way as /θ/ and /ð/! alzhough, a very similar sound, zhe voiceless linguolabial fricative, can be made by pressing zhe lower lip against zhe alveolar ridge, or against zhe base of zhe shelltoozh. zhis sound is obscure enough zhat it doesn't have a symbol in zhe standard IPA, but zhe extended IPA uses f͇ to represent it. furzher investigation into nonhuman phonetics will likely require zhe creation of more unique symbols and phonetic designations.
bonus question: "why do you use "zh" for both sounds? isn't that ambiguous?"
yes, it is ambiguous! "th" in standard english is ambiguous in exactly zhe same way. welcome to spelling lmao
