Before chat models, I did something similar with Google Translate, but GT doesn't tell me why things should be different; and worse, GT tends to auto-correct typos, leading to stuff like this: https://translate.google.com/?sl=de&tl=en&text=Schweinwerfer...
("Schweinwerfer", spelled like that, would actually mean "pig thrower": Schein (shine) vs Schwein (pig))
I think to be a real "coach" they'd have to be able to push you proactively. You can script that kind of thing, but if you're getting that done, maybe you don't need much pushing.