To give DPC some credit here, he is not a native american. He is swedish. Many swedish people are speaking very very good english, they learn it in school VERY early (basically starting in kindergarten) and english is basically there second "mothertongue" But its different in terms of how they use english like they do in the US, especially in more or less "lowlife" neighborhoods. English in Harmlem (or like someone mentioned Bronx) is something totally different like using English in Stockholm.
Movies and books can get you only "that far" to get it right how people in the US are talking to each other if they are coming from different lifestyles.
Iam german and i sometimes notice too that its not really fitting how character sin being a dik are expressing themselfs. But i couldnt do better. and certainly no one other on F95 can either. I dont know a single DEV around here who is from the US, most are more like east-europe and you can read that... "engrish" is mostly common
DPCs english is VERY good, and he really trys to be as close as he can to write as he thinks people at that age expess themselfs. And he is very close i think.
Even in most US-movies i think all the time to myself "come on, no-one in the age between 18-22 talks like that" (and though iam german, most of the times i watch movies in OV)
I think its just as simple as this: to talk by yourself is VERY different if you try to WRITE how people talk. Most people couldnt even write how they used to talk by themselfs.
My written language (in german) is VERY different to the way i talk... so its really difficult to get it very realstic all the time for many different chracters.
Mostly DPC gets it done very good in this game... sometimes not. And yeah the "serious talk" with Quinn (only on her path) was a bit off, serious and sad or not... she wouldnt use words like she did there in some places. But... meh... it didnt really bother me.