This was a really good explanation! I'm also learning Japanese and these little nuances are really fun, so thank you for taking the time to explain it! How many volumes of this manga are there?
Pretty sure scanlators chose the one that sounded more natural in English. We would never say "I want to marry them...!" unless the person we're dating is agender or nonbinary or prefers they/them pronouns. It's too awkward to phrase it like that; scanlators definitely chose the better translation (iirc they have lived in Japan most of their life or a long time at least so I trust that they know what to say)
So, I’ve bought and read Sasaki to Miyano’s Japanese physical copy and realized that this English scanlation was really good, but I thought it’d be good to point out this one thing...
In Ch.12.5, last page Kagiura (the roommate) said “I want to get married”. That was not wrong, but something was lost there. This conversation was more like from the clubmate’s perspective. (The clubmate who asked “You’ve got a girlfriend?”)
What I mean is...
In the Japanese version, Kagiura said “結婚したい (Kekkon shitai)” this sentence is a bit vague and can have a double meaning. Depending on the person’s who listen, It can either be “I want to get married” or “I want to marry (him/her)”
From the classmate’s perspective it went like this....
They were practicing basketball, then suddenly, Kagiura blurted out something about getting married (Kekkon shitai), which have a vague meaning and anyone who do not know of the context will automatically take it as “I want to get married.” hence the classmate took it as Kagiura saying he wants to get married.
BUT
From the reader’s perspective it went like this...
Hirano woke Kagiura up, and obviously spoiling the hell outta him. Then when Kagiura leaves the house, Hirano gave this bright smile, Kagiura blushes then the scene jumps to Kagiura in school saying “Kekkon Shitai”. Which any readers will take as “I want to marry him.” It was like, Kagiura remembering about the Hirano of that morning, and the happenings of that morning makes him want to marry Hirano.
(It’s a bit confusing, eh?)
Maybe you’ll understand if I use this example...
If you’re watching/reading Attack on Titan, Reiner would often say “I want to marry her.” in his mind when she faces with Krista, because he likes her, right? In Japanese, Reiner was saying “Kekkon shitai.” Kagiura’s “Kekkon shitai” is the same as that. XD
Japanese can be very complicated at times, but that’s why it’s fun because the authors can make a lot of gags using the Japanese language’s complicatedness. But unfortunately, foreign fans misses a lot of those because it’s almost impossible to deliver them using the English language, but I hope this explanation somehow helps.