So for Daeran, compare: "Прекрасно..."Дейран избегает смотреть вам в глаза. "Мне дали еще немного времени повоевать с отвратительными демонами в самом отвратительном месте Голариона, чтобы потом упрятать в застенок. Можем мы наконец уйти отсюда? Это место... меня нервирует" vs "Just wonderful..." Daeran avoids looking you in the eye. "I have been granted a little more time to keep fighting heinous demons in the most heinous region of Golarion, so that I may then be incarcerated afterward. Can we finally leave this place? It... unsettles me." NO. NYET. In the original, Daeran shifts registers into ironic colloquialism and deliberately is written as petulant. Most of this is lexical choice, in this case, but compare it to a closer register-focused translation below (how I'd go about it anyway, feel free to make suggestions):

"Marvelous..." Daeran avoids looking you in the eye. "They've given me a little while longer to fight revolting demons in the most revolting place in Golarion before tucking me away in a dungeon. Can we get out of here already? This place is..." He looks away. "...rather trying." Note here that нервировать is a marked calque in Russian. It's not "this place makes me nervous" or "it unsettles me", the fact of it being a calque from French gives it a very specific connotation regarding that KIND of person who would use it. This is a social register (a kind of aristocratic euphemism/understatement, it's a bit "precious" in the French literary sense of préciosité, as in performing refinement). TLDR: By not attending to the sort of register Daeran uses, the characterization changes from petulant (perhaps ironically so, but still petulant) where he is using both colloquialisms and hyperbole and understatements to convey his state of mind, to frankly kind of flat. To my ear, it's losing a fairly important layer, especially in the emotional context of that quest. And then we have this: For Regill, compare: "Ты чем-то недоволен, преступник? К тебе и без того уже проявили слишком много снисходительности. Командор, он опасен и даже не помышляет о раскаянии. С ним следует покончить здесь и сейчас."

vs "You dare to complain, criminal? You have already been shown too much leniency. Commander, he is dangerous and had no intention of repenting. He should be dealt with here and now."

Huh. No. Nyet. Those are just quite significantly different, starting with what tense is used. So a closer translation that conserves Regill's register and speech pattern would be something like this: "Something displeases you, criminal? You have already been shown more leniency than was warranted. Commander, he is dangerous and does not even contemplate repentance. The proper course is to end this here and now."

During Regill's final trial, (and should that trial go well), he offers the MC an explanation. In the English version he says after mentioning the Bleaching: "A shortage of time pushes one to extreme measures, and I am no exception." (Sorry I'm not at my desktop so can't link the screenshots). This "I am no exception" caught my eye because it is completely absent from the Russian language version, and in fact there he says something quite different. I'd translate it like this: "A deficit of time nudges one towards extreme measures. It is such an extreme measure that I utilized here." The meaning, as you can see, diverges, and so does the impact, and changes some of how the whole topic of Bleaching landed with me, in the dialogues, banter, and lore bits you find in the game. If you're like me and like to make mountains out of linguistic molehills, I'd say that the English version of Regill experiences Bleaching as something that is happening to him, but as he says, he makes "no great fuss" of it (in Russian, he uses "problem" instead which has a different connotation to my ear). With the English version one gets the impression that he refuses, on principle, to mitigate the Bleaching, since to do so would likely be inherently chaotic (since that is after all his nature as a First World critter, and he mentions that many other gnomes go to great lengths to do so, which he finds unpalatable). The Russian version, on the other hand, sounds far more strategic or agentive about it, by extrapolation: if a deficit of time nudges one to extreme measures, then one might ask, does Regill find extreme measures useful, and thus the Bleaching also useful in a certain sense? From there, is he weaponizing it perhaps? it certainly sounds like this is what he implies in that sentence. After all, the awareness of one's finitude is a pretty big topic in the game as a whole, as we see with Daeran as well. So to me that puts Regill a bit out of the pragmatist camp and more into the existentialist one, at least in the Russian version, as far as characters are concerned. This, in turn, is in interesting dialogue with his ending slides on both the Aeon and the Trickster paths. So now onto Inheribro. I won't bore you with the minutia—but there were some moments in the English version, especially in the back-end of the Angel questline where you free him from goat boy, that kinda felt emotionally flat to my ear, so that was the original motivation to switch languages and see whether this is a problem of translation. Turned out, he just sounds quite different across the board. In English he kinda has one register that seems to indicate his general celestial lawful-good angelic self. In the Russian version, he's got multiple registers, depending on what he's talking about: conveyed by syntax and lexical choice. And then some translational decisions really just made me raise an eyebrow. For example, in the English version, he refers to the KC as "Champion." In the Russian one, he calls them "Protector" or "Defender"—that's a really different connotation, once again, and a totally different emphasis at least to my ear.

Add to this inbuilt differences in syntax that simply don't translate across languages: Russian distinguishes between formal and informal you (often called the t/v distinction in linguistics), and that distinction carries quite a bit of meaning. In English, this is flattened into a general you, without differentiation, so the nuance—like when formal switches to informal, conveying, in different contexts, rank, or intimacy, or age—it can carry quite a bit of added nuance (and sometimes packs a real punch). For example, when as the KC you speak to Liotr, you address him with the informal you, and he addresses you with the formal one, denoting rank. During Regill's trial, the KC actually switches to what appears to be the formal you, whereas before they both spoke to each other using the informal/intimate one. Regill, for his part, barely addresses you at all, other than in third person during that bit, and often using subjectless sentences which Russian allows, but English doesn't. And then, when he challenges the KC to a duel, it is a direct, informal you address. It's hard to convey just how much whiplash that produces, linguistically.

I hope that gestures at an answer!

Ok, now firmly in the realm of my own personal headcanons, with my own personal sociolinguistic nerdery hat on, and that's dangerous territory because I could muse about this for hours. So I'll try to just pick one thing to focus on: regional dialectical variation, as per your question. I would expect (and really, how I write it/love seeing it in fic) different sociolects (with some sort of phonological specificity eg accents) mostly based on geography/cultural "cluster"; socioeconomic class; and if we want to get granular, occupation. So say Rift sociolects would sound differently from Reach sociolects, as an example—phonologically, maybe somewhat syntactically, definitely in terms of stock expressions, just by virtue of their geographic locations, unique linguistic influences so on. I would absolutely expect language gradients (which is that thing where a population shares a particular linguistic code, but as we move geographically from say one village to another to another, we will see differences until we reach the point where it takes a huge effort to understand each other because the codes have diverged enough, in which case another, shared "trade" language kicks in to pave over). Considering what we know of TES linguistics and history, I'd expect at least some degree of bilingualism for many of the characters, and as always with bilingualism, I'd expect a great deal of code-switching, loan words, and calques. How code-switching would happen is another can of worms and I can talk about it for hours, but I will exercise Chill and just vague-gesture at it. I'll also vague-gesture at language standardization and what processes might be happening around that with the Empire's waning influence.