We’ve all had our share of frustrations over individuals who either think they know English (but they don’t) or know they don’t know English (but still “translate”).
I agree with @lutra that a report button could be misused and abused. But perhaps a standardised form at the help centre webpages to show evidence of deliberately wrong translating or using third-party translation engines?
We’ve also had an alternative discussion on another thread. Instead of punishing negative behaviour, we could reward the positive one by rating the quality of translations.
This is an on-going issue, so here are some threads about it that I know of: