New pet peeve: when people have characters with accents in works of fiction and have the accent persist when the character writes (a) or has internal monologue (b).
if i may, i believe you're talking about two different things. allow me to expand.
point a: i believe that this is what's known as cultural linguistical differences. when you come from place a you talk differently from place b based on upbringing, local slang, etc. so that makes for a cultural shift. easy example: letipex and i both speak french-french (not québécois, ivoirian, cajun...). so we share a language only separated by local accent. however, he's from the north (paris), and i'm from the south (toulouse). the accent is a big change when speaking, but you can't really translate it into writing without butchering the spelling (in my case, i'd probably need sheet music to do it anyway). however, the local slang is a big factor, going so far as to swap out words for one another.
this pastry, for example, is the longest-running joke between northerners and southerners in france. tipex most likely calls it a "pain au chocolat", i call it a "chocolatine". based on this, you can surmise that someone who is writing will use his "local accent" out of convenience rather than try and wilfully use the most neutral ways of saying something. i'm not even going into local pride here. this is just instinctive writing. hell, i'm sure you and askold have some variance in writing when writing in finn.
so point a can be explained, if out of a more "transliterative" way.
point b is going to be a lot more biased from case to case. and in my examples, i hope i don't mix up where you guys come from. if so, i apologize in advance.
zygarde is from louisiana, which has a very distinctive drawl (distinctive even from the rest of the south). that's the accent she's heard all her life, and chances are, she picked up traces of it. she can fully understand "standard neutral" american (california or d.c., take your pick) just fine, but chances are, she won't speak it unconsciously.
queen outright stated she's got a strong local accent (southern too, i believe). unless she came from louisiana too, she won't have picked up the same accent that zygarde has, and by reading into her posts, i'd hazard a guess that she tries to mask her accent, so as to mask her roots and sound more serious. because it's how we learned to talk, we adopt the local accent, until the local accent becomes our norm.
that's why people like art (australian) will sound different from conty (brit), from spaceprog (georgia?), from ghoti (minnesota), from ironchew (new mexico), and from you.
now ask any of those people i mentionned, and their accent is the one they speak with in their mind. just because it's their baseline norm. because i'm different, i monologue in yorkshire english, but speak in virginian. i learned to speak in virginia, but the rest of my family speaks in a northern english accent. i can do the yorkshire accent, but i have to think about it, it's not a reflex like slurring the words i usually do. my baseline is yorkshire english, can't do anything about this.
hope that clears up a few things.
disclaimer: in no way do i pretend to know intimate details about the people i named, especially not their speaking habits. this is all surmised, hypothesized, and assumed from their geographical information i found on this forum. if anyone wants to disagree, feel free and i'll update the post.
