I definitely side with DYWYPI on this one - trying to shoehorn in English accents in place of Japanese dialects has always been a distractingly bad thing to me. As s/he rightly points out, an accent brings with it a lot more implications than just "different way of speaking than standard." It conjures a whole host of cultural connotations and prejudices (in the neutral dictionary sense of that word). There is never a direct analogue between what a particular speech affectation in Japanese connotes and any English accent. I definitely think it does more harm than good to a character no matter how integral it is to the characterization.
In this particular case I would much rather see her just speak notably more casually/coarsely in standard English during her "dialect times." That alone is enough to communicate effectively enough the dichotomy between her "put-together, type-A overachiever" work personality and her incongruously rough "real" (for lack of a better word) self.
FWIW I won't be reading this translation for the above reasons, but props at least to the translator for giving it this much thought. I just really disagree with the result.
The translator's Scottish accent attached to this kind of ruined it for me and was comical (not in a good way..), but its a free translation and managed to get the plot from A to B.
