The question A confusing use of a negative seems like it belongs on English Language Learners. I was considering flagging it for moderator attention and choosing a custom reason to say this. But I'm unsure if this is the proper course of action because it's probably not off-topic on ELU (or is it?) and because ELL is a beta site. So should I flag cases like this or leave them be?
Since the user who asked that question said to be learning English, the question could be a candidate for migration. That doesn't mean it will be migrated; poor questions are generally not migrated. (The motto is, "don't migrate crap.")
Flagging for moderation attention to suggest a question to be migrated is fine. The moderators normally consult the moderators of the other site, and if they don't want the question to be migrated because there is already a similar question, or because it is not a good fit for the site, then the question will not be migrated.