If I write a story about Charles II and his time and someone in the story sais: - "The present King of France is bald"- how would the logician guys explain the difference 'logical-unlogical?

Well, if it's a story, instead of a history, they might say it meaningless. Not sure. Context is always important. I believe the problem goes away if France is a monarchy at the time of writing or uttering and the present King is bald.

I guess I posted my thread mainly because I've been thinking about how complicated language and communication are. I've never much been bothered by the "present King of France is bald" kind of paradox (enigma?), but there are / were people whose opinions I respect who are / were obsessed with it. And, my point about the "present King of France is bald" is that whatever its problem(s) may be, it has nothing to do with grammar. The sentence is perfectly grammatical. The problem may have to do with situational semantics or logic or pragmatics or who knows what.

Ceci n'est pas un seing.