I've seen that as well. I think its still valuable to point out that the text feels like LLM text, so that the person can understand how they are coming across. IMO a better solution is to use a translation tool rather than processing discussions through a general-purpose LLM.

But agreed, to me the primary concern is that there's no disclosure, so it's impossible to know if you're talking to a human using an LLM translator, or just wasting your time talking to an LLM.