I find it easier if everyone writes the language(s) they are confident in. Then it will always be possible to translate it. If someone is writing in a language they do not know, with or without the help of automated tools, the result may be unparsable. Example:
Requiring people to post bilingual texts is not preferable to having a forum bot that adds translations on request.
There are posts in many different languages on these forums and it was reasonable for the original poster of this thread to assume that posting in a non-English language was fine. I think it is fine.