Not gonna lie, that triggers some headcanon with 'Armpit-Pussy' where the armpit litterally gets pussy inside.
Or these weird pictures with 'Dick-Nipples'.
Don't ask, I wish I wouldn't have seen some things.
As someone else pointed out, it is clearly something that comes from the language (translation). It's because the mindset is that the sexual organ is the vagina/pussy, so any other "hole" used for sexual use becomes a "pussy-something" or "something-pussy".
It's a bit like if one translated "guts" (as in "having the guts to") literally in some another language, it would not make really sense because it would really refer to the intestines, while depending on the context and exact situation, it should instead be translated rather either with "having the stomach" (this how it would literally sound back-translated to English), or "having the testicles" (though the word used is not so polite, of course).
It is also why your reference to Ass-Mouth-Pussy does not work, it is not a reference to three guys (or tentacles, or whatever) as already explained by others, ass-pussy and mouth-pussy do not refer to a "double penetration" or a "spit roasting" (those are the terms used, AFAIK), but simply respectively to anal and oral sex (though they may also be used in a context of double penetration and of spit roasting).
I admit the "armpit-pussy" I missed, maybe I have not played "Karryn" in too long
As far as translations from Japanese go, Karryn is by far not the worst, despite the quirks.
Plus, let's be honest, I have seen even real movies with a solid budget (millions) from Hollywood having dodgy translation, or movies that had a title in English and a completely different title in other language, even if they were relatively easier languages to translate to like Spanish, French or Italian, so, cannot be expected that a smutt game can find professional-level translation that can also appropriately translate this type of vulgarities, even because it would be difficult to find a professional translator that would know it in both languages, and more importantly, admit they know it by working for it.
In a way, it is a form of hipocrisy, but if a translator tried to get work from a big bussines or public organisation listing as one of their translation works having translated Karry, they may not really get a good reaction ;-).
