So i just checked this Tsumamigui 3 out and gotta say it is perfectly hookable, so it it's not a problem to extract text out of it, may be its a problem to pack translation back, idk.
Judging by first few dozens lines that i checked it is quite intelligible when deepl'd, idk what that guy did with it with his deepl translation but it does seem worse. Not to mention that japanese itself is nothing special, there are much much harder VNs out there, and hiring native to translate it is clear overkill. Nukige (porngames) tend to have rather simple japanese, so no surprise there tbh, heck even I can read it quite comfortably with dictionary and i'm only beginner, so yeah, i'm pretty sure you overestimate the problem.
The only problem i can imagine, is when woman is moaning usually her words are interjected by moans or cut short, so you can see only part of words in kana (japanese alphabet, contrary to "kanji" - hieroglyphs) and you kinda have to guess what she tried to say cause it is not parsable, but i would say that is not a biggy even if you miss them a little.
P.S. it's not even that long as a VN, sure 40 hours is alot for nukige, but for VN it is nothing special, for example Fate/stay night(i mean single game) is more then twice as long.