I recently saw for the first time (via Netflix) a Japanese film from 2002 entitled Twilight Samurai (Tasogare Seibei). It's a wonderfully restrained and down-to-earth portait (reviewed here and here) of a dutiful but impoverished petty samurai aching to live as a plain farmer (not—like Tom Cruise—aching to die with The Last Samurai).
But an added attraction for me was the combination of English subtitles and a Japanese regional dialect, Yamagata-ben, or at least a Shochiku Film rendition of some of its key features. The dialects of the northern (Tohoku, lit. 'northeast') part of Honshu are collectively known as Tohoku-ben, or somewhat less diplomatically as zuzu-ben for their failure to distinguish /i/ and /u/, rendering both as a high central unrounded vowel [ɨ], which then of course fails to palatalize /s/ and /t/, so that sushi, shishi 'lion', and susu 'soot' all sound something like [sɨsɨ], which can be spelled susu, since /u/ is not rounded in standard Japanese either.
I haven't been able to find much online in English about Tohoku-ben except for a few sketchy accounts, the most extensive being a sketch of Miyagi-ben by a former JET volunteer. (Yamagata prefecture is on the Japan Sea side of Miyagi prefecture in southern Tohoku.) So I thought I'd offer a few general impressions of (Shochiku emblematic) Yamagata-ben from my second viewing of the film.
/s/ > /h/ in suffixes – I noted the kin terms otohan 'father', okahan 'mother', and babahan 'grandmother', the names Tomoe-han, Naota-han, and the polite expressions gokurou-han 'thank you', oboete-naharu 'do you remember?', and oyu wakasute kumahen 'can you boil some water for me?'. This lends a Kansai flavor to the dialect.
/ai/, /ae/ > /ee/ – This is not uncommon elsewhere, but it generally signals plain—even rough—talk. In Yamagata, it also occurs in polite speech. In the film I noted omee 'you', deekiree 'really don't like', and nee 'not' (as in sabusukunee 'not sad').
/-masu/ vs. /-masunee/ – Polite negatives in Yamagata-ben sound like affirmative confirmations in standard Japanese. I noted ikimasunee 'won't go', mattaku arimasunee 'absolutely don't have'.
/ne/ = /no/ tag – Yamagata no(u) performs the functions of the standard Japanese tag particle ne(e). In the film, I noted yoi ko da nou '(you're a) good girl, aren't you?'. (My usage tends toward /na/, thanks to my high school days in Kansai.)
/e/ > [i] – The backing of the high front vowel /i/ to [ɨ] (and its merger with /u/) leaves room for the mid front vowel /e/ to migrate upward. I noted sinko 'joss stick' and madi, madi! 'wait, wait!'. However, there were plenty of unraised /e/ as well, so I suspect the actors were pulling their punches to maintain intelligibility and relying instead on just a few emblematic raisings to give a flavor of the dialect. (This is true of most, if not all, renditions of "dialect" on stage and screen.)
de gozaimasu > de gansu 'the polite copula' – This remapping was so strikingly regular and transparent that I suspect it was not just one of the more salient emblems of Yamagata polite speech, but one of the easiest for dialog coaches to teach: owasure de gansho ka 'had you forgotten?'; sou de gansuta 'yes, it was'; omoe-dasu no wa iya de gansu 'I don't want to think about it'; ayamaru no wa ante ho de gansho 'I'm not the one who should apologize' (I'm not too sure whether my ante ho should be anta no hou 'your side' or hantee hou 'the opposite side'). However, I did catch one instance of de gozeemasunee 'is not' (= de gozaimasen).
/-t-/ > [d], /-d-/ > [nd] – Unvoiced obstruents tend to get voiced medially, while voiced obstruents get prenasalized. I didn't hear a lot of this. Maybe it would reduce intelligibility too much for the audience. Among the examples I noted were: odohan 'father', todemo suzuree 'very rude', and madi, madi 'wait, wait'.
Finally, the grammatical construction mou ii de ba (= mo ii deshou) 'that's enough, isn't it?'