Ok...how about this food for thought. Your going out of your way making this hella swearing filter system that in the end, slows down the server and people (/point Alien, <3 you! ) can STILL bypass it anyway.
Just do this. Add a new feature in the User Account page...LANGUAGE FILTER.
It'll accomplish the following. People will STOP trying to go through the filter, thus less code to prevent people to go through it is required. If you want to get away with swearing, turn off your filter! Simple if then statement.
Those who have sensitive eyes (ie: wuss) and strain and cry when they see a cuss word won't even have to worry about people going through your efforts to keep the boards clean.
Come on, it can't be that much of a shitty idea.