This goes to the heart of an issue in linguistics that I've been thinking about lately. Linguists talk about deep structure and surface structure. Surface structure is the actual grammatical structure of a particular sentence or phrase or utterance as found in reality. Deep structure is the so-called "kernel" sentence or essence that underlies the surface structure. A passive sentence is the classic example. According to this thinking sentences 1a and 1b have different surface structure but identical deep structure:
1a: Wild Bill Hickok was shot by Jack McCall.
1b: Jack McCall shot Wild Bill Hickok.
Linguists who believe in deep structure say that the semantic value (the meaning for lack of a better term) of these phrases is identical. Linguists who don't believe in deep structure might deny this.
In Deadwood the use of anachronistic language assumes that modern swearing has essentially the same deep structure as the swearing of 1876. Therefore replacing one with the other is actually a faithful way of translating. But I wonder, and here is where deep structure becomes a problem, if there isn't something else going on apart from semantics and if that something else might not be the same from 1876 to 2009. Like I said, I'm still thinking about it.