So this dialect thing, if it's caused the kouhai trouble the entire time, why introduce it after 10 chapters of them communicating just fine? It makes it really hard to believe, that the senpai sometimes talks in a dialect while at work without realizing it, which seemingly creates communication problems if it isn't introduced in the early chapters. And it also seems to be gone the moment senpai's mom is gone, because the story between senpai and kouhai didn't and doesn't need this.
If, by chance, this was due to the tl completely changing any dialect in the previous chapters to regular english, then that's a different case. But I can't even remember any situation in the previous chapters, that showed a miscommunication based off that dialect "problem". Maybe I just missed it though.
Don't mind me, just a comment about this being a nice manga...