I'm wondering whether it's necessary to have pages on words like this. On one hand, it's an important word, but on the other, it's the kind of word that quickly changes as people come up with new ones. In English, we have dozens of words that can mean stupid: moron, jackass, nitwit, dumb, retard, etc. So I think that even if such a word is not created for an IAL, people will rapidly come up with many imaginative candidates!

The same in French... But idiot has also a medical sense: a person of IQ not above 20, and unable to speak.

I think words like this are needed. "Idiot" is as important as "genius". Besides, "idiot" and "dumb" have survived centuries in English. People can come up with new imaginative words, but it's good that there's one in the dictionary to aid people who don't have that much imagination or courage to coin their own words.
I didn't mean the medical sense of the word, you should add another table for that.

I found that the medical sense is now obsolete...

It's difficult to translate such a word. I never use "idiot" in my daily life, despite I can understand it. The more widely used word for a "foolish person" is "con" (Jens certainly know it ;-) The problem is that "con" is not very international.

That's OK. The words don't have to be international, just common French words. I remember seeing a French movie where one dude said often "Quel con!" or something like that. :-)