I can't read Russian, but isn't "dern" in this context more likely to be a version of "darn" e.g. "them derned varmints"?

Yes, but the OED says "see DERN a," where "a" means "adjective." Of course it occurred to me that dern = darn was a more likely source, so I went to that entry and there was indeed an 1876 quote, but it was this:
‘MARK TWAIN’ Tom Sawyer vi. 56, I wouldn't give a dern for spunk-water.

Which isn't much help.

@Kate M.: The OED has a few different entries for "dern", but as far as I can see, only one has an 1876 quote, and it's for a noun sense, not an adjective sense. Further, the quote doesn't seem relevant:

1876 ‘Mark Twain’ Tom Sawyer vi. 56, I wouldn't give a dern for spunk-water.

You want the later entry that says, dern, U.S. var. DARN a. That has the 1876 Twain quote with both dern and druther.

1876 ‘Mark Twain’ Tom Sawyer ix. 97 I'd druther [rather] they was devils a dern sight.

I suspect, given the date, that it's a contraction of "had rather" rather than "would rather".

@MMcM: Odd, that doesn't seem to be in the OED Online. Searching for entries with "druther" in quotations, all it pulls up is the entry for "druther".

But is 'druther' a word? For me (who uses the phrase 'If I had my druthers' a _lot_) it's always 'druthers' and 'druther' sounds decidedly peculiar.

Odd, that doesn't seem to be in the OED Online

Odd indeed; thanks for finding it, MMcM!

I suspect, given the date, that it's a contraction of "had rather" rather than "would rather".

The OED says "would rather," and that's good enough for me.

Michael: I agree, it's only "druthers" for me too, but the English language is older and bigger than both of us.

I'm not a great believer in 'synchronicity' (just a more 'woo' name for the recency illusion), but I saw this expression used just the other day on one of my regular haunts (but Pharyngula and The Bad Astronomer both come up blank, so I have no idea where it might have been). I did have to stop for thought, but I understood it quite readily. (But perhaps I've just come across it before in a more obvious context and promptly 'forgotten' about it.)