> It may present more fluent text, but if it doesn't know it's strayed from the source text and you can't tell either (because you don't understand source language) then you'll end up with error-laden pseudo translations. At least with NMT you know the errors are consistent.

To be fair, this is an infamous failure mode of neural mtl too, and a big part of what makes the discourse around GPT so ... evocative of the discourse in 2017.