I think in the year 1700 there were still a few adults in Cornwall whose usual mode of communication among themselves was the rapidly dying Cornish language, but only a tiny number of children could speak Cornish by that time. In the late 18th century, it was dead.
The series of novels about Ross Poldark, and the TV series inspired by them, is set in Cornwall in the late 18th and early 19th centuries.
One peculiarity of language used in the TV show is the use of subjective forms of personal pronouns (I, we, he, she, they) in instances where in standard English the objective forms are used (me, us, him, her, them).
Our servant lives here in this house with we.
I saw she yesterday.
and so on.
How truthful is that? Did people in Cornwall at that time normally do that? Is that actually an influence of the Cornish language?