Is it illegal to slander someone over the internet on a "slander" site?

Yes if the claim is false and it was said to someone other than the claimant (ie broadcast over the internet).

The correct term would libel. Slander is only used if the statement is spoken not broadcast or published.

thanks. Was trying to think of “libel” but it drew a blank. The claims were not false but true or false would take months to prove. And he wants to sue when the “defendant” has no assets at all. I guess that means he doesn’t know what he’s doing or it’s just an empty threat.

In cases of libel the point of suing is not to get money as such but to clear your name.

If the claims were proven to be true then it’s not libel, however the burden of proof would lie with the defendant.

In Germany, yes. People were convicted for this.