Archaism in dialogue - what's it doing there?

This week, I've been scanning through all of the novels and collections published in the year 1832. Although I'm looking for representations of dialect (and have found several), I've also noticed another kind of non-standardness - archaism - in some of the dialogue between characters in these texts. Rather like dialect representation, this archaism is markedly different from the main narrative style (which is, as you'd expect, fairly high-register, standard English). It occurs to me that the author must make a deliberate decision to present the characters' dialogue in this way - much as is the case with dialect representation - but I'm wondering what this archaism is doing there. What purpose does it serve? Is it connected to issues of propriety (as in 'novel-of-manners' style) or is it simply customary for this period? Or is there another explanation? Here's an example from a collection of short stories, Dramatic Stories by T. Arnold, esq. in Three Volumes (1832) - any ideas, thoughts, or comments welcome!

The third short story from Vol III - 'The Conscript and His Dog' (available online: http://www.archive.org/stream/dramaticstories03arno#page/73/mode/1up) concerns a French farming family who take in and bring up the daughter of a friend (Ariette) whose mother has died. She later marries the son of the family (Louis), while his twin brother (Jean) heroically takes his brother's place in the annual round of conscriptions, in order to enable Louis to marry Ariette. Included also is an incredibly sentimental tale of Jean's devoted dog, Rollo (oh my - I nearly cried). Although it's set in France, and discusses language (Ariette, for example, at age 2 was 'prattling with all her might and main in a patois, half provincial, and half of her own making', and later is described as 'thorough French') there is no attempt to represent this in the dialogue. There is an acknowledgement of transliteration too - after the father of the boys, Gavard, says 'cursed name of a pig', the narrator's voice notes 'There is nothing like the literal translation--especially of oaths--and such the above exclamation of Gavard was meant to be'. It strikes me as slightly odd, given the French setting, that English archaisms crop up in conversations. Pronouns are especially interesting - Louis and Jean often use 'thee' and 'thy', as here: "Dear Jean! dear brother! my best friend thou art--I will follow thy advice, for I am sure thou know'st best [...] and now, apropos, Jean, what is thy secret?" There's altogether a good deal of 'hark' and 'thou know'st thy' and so on in conversations between these two. Ariette also uses these forms in informal conversations. Gavard addresses his sons using 'thee', yet Louis switches to 'you' when talking to his father.

Is this perhaps a hangover from the Early Modern English use of pronouns to denote degrees of formality? 'thee' informally' and 'you' formally? Just a thought. However, that doesn't explain the 'art', 'dost', know'st' forms of verbs - they're used in dialogue, but not in the main narrative text.

Any ideas?