But I genuinely didn't know that other countries do things differently. What does defamation even mean if it doesn't include the concept of untruth?
FWIW I'm only really familiar with the American usual.
Words can have multiple similar definitions with small variations. If I look up "defamation" I get:
> Defamation is a legal term that refers to any statement made by a person, whether verbal or printed, that causes harm to another person’s reputation or character. --- https://legaldictionary.net/defamation/
> Defamation is a communication that injures a third party's reputation and causes a legally redressable injury. The precise legal definition of defamation varies from country to country. It is not necessarily restricted to making assertions that are falsifiable, and can extend to concepts that are more abstract than reputation – like dignity and honour. --- https://en.wikipedia.org/wiki/Defamation
English libel law is an evolution of the former English law known as scandalum magnatum -- "scandalizing the mighty". Basically, if you say bad things about powerful people, those powerful people will crush you with the law.
As an example, Robert Maxwell embezzled millions from his company's pension fund, and also used that money to sue anyone who slighted him - including anyone who said he was embezzling from his company's pension fund. He was never prosecuted for embezzling millions from his company's pension fund.
He escaped that. By dying. Probably suicide.
The walls were closing in
I don't like the idea of prosecuting people for this, but I don't think it's illogical.
Perhaps you mean slander/libel?
Libel = defamation in writing. Slander = defamation in speech.