There some limitations/known issues in the underlying blacklist:
https://github.com/splorp/wordpress-comment-blacklist#known-issues-limitations--other-gotchas
Maybe we can solve them if we provide more options like:
- add URL shorteners
- add WordPress stuff links
- add non-english keywords
Although I don't know how to extract these strings which are all in the big blacklist.txt file.
And we shouldn't overwrite manual added strings:
https://wordpress.org/support/topic/manual-blacklist-overwritten
Maybe we can just append them to the manual added ones.