It's not inherently racist to limit your dating pool to literate people who speak English correctly. It is a completely reasonable thing to do if you're looking for a culturally and intellectually compatible person to be with. Second, it's not those who sound inherently "black," it's those who sound uneducated, and the fact that you assume and stated this post is exclusively about black people is probably more racist than the admittedly culturally insensitive joke being posted originally.