Web discussion moderating software

I'm hoping someone can steer me in the right direction.

I'm currently designing a website that I'm hoping to use so that I can get affiliate commission. In that website I'm going to have a discussion page and I'm hoping to find some software that I can use that will help me illiminate certain things i.e swear words, racist slurs. I thought the best thing if I could find it is some sort of software whereby it will change certain words to other words automatically. For example if someone puts in a swear word it will change it to a non swear word i..e Fu** to flower or if someone puts in a racist slur i.e Nig*** it will change it to successful and beautiful african american.

I hope this makes sense and if someone knows of software that does as I have described and it is not too expensive, then please steer me in the right direction.