Got it - that makes sense, and I can see how that would be a way for people to work around spam filters.
As a workaround, while we figure out the nest way to handle this in core, if you add that unicode character as a watched word, it will get flagged in posts. Just go the page you linked, hit the copy button there, and paste that in as a new watched word to flag. That will cause any post using it to be flagged for review. I just tested that and it works correctly.
While there are legitimate use cases for using it (like adding some text from an RTL language inside other text), it is certainly a potential spam vector. Adding it as a watched word will help you identify when it is used and review the posts as they come in. In the meantime, we’ll see what would be the best way to handle this in core.