What are the legal differences between an explicit insult, that qualifies as slander, and an implication of the same insult?
I am a German citizen, so I'd prefer answers applicable to Germany. But any other jurisdiction is fine also.
If I understand your question, you're asking the difference between something like this:
"You shouldn't do business with Bob; he's a child molester. Raped a whole bunch of kids. Everyone knows about it."
"You're thinking of doing business with Bob? Huh. That's your call, of course. I won't say anything against Bob. But Bill is in the same business, and I happen to know that Bill has never molested any kids."
"There are three people you could do business with. There's me. I've never molested any kids. There's Bill; he's a little expensive, but he's never molested any kids either. Then there's Bob. I don't have anything to say about Bob."
I don't know the answer under German law, but under U.S. law, it's surprisingly complicated, and varies by jurisdiction. Here is a thorough but somewhat dated article on the subject.
New York has recently established an explicit test for defamation by implication:
To survive a motion to dismiss a claim for defamation by implication where the factual statements at issue are substantially true, the plaintiff must make a rigorous showing that the language of the communication as a whole can be reasonably read both to impart a defamatory inference and to affirmatively suggest that the author intended or endorsed that inference.
Stepanov v Dow Jones & Co., 2014 NY Slip Op 03940 (App. Div. May 29, 2014). That opinion also discusses the other approaches used in other U.S. states.
Under that standard, it seems clear that my example statements would be defamatory; any juror would immediately understand both the factual implication and that it was 100% intentional. In practical terms, I doubt any court in the United States would not consider them defamatory.
In general, defamation is harder to prove in the United States than in other jurisdictions, because of the strong protections afforded to speech under the First Amendment--but I don't know enough about German law to speak to that issue.