English is actually a pretty lame language... It's got plenty of rules, but it never follows them. You can't really "learn" English, you either speak it or you don't. That's because you need experience with it in order to figure out all the idiotic pronunciations or spelling oddities... "Through" is one of the most ridiculous words I can think of.
Esperanto is supposed to be the easiest language to learn and use efficiently, but nobody does. It's a scientific language, rather than a cultural one. Therefore, there's no tradition-linked reason for someone to learn it.
I've been trying to find an IQ test to bugger around with lately, but the likelihood of finding one even halfway decent on the internet is pathetic... I took one, but that turned out to be utterly bogus. Seems you just have to find some official place to take one...
And yeah, it is indeed a bit difficult to accurately test something when you don't know what you're testing for. I was reading an article about intelligence and how people will generally interpret ability in local cultural values as exhibiting intelligence.
Myself, I always considered intelligence to be the ability to learn. Being able to wrap your mind around new concepts or simply learn something new with ease. And not just memorizing, actually learning something. Finding out how and why it works.
This is in contrast with knowledge, which is the stuff you've already picked up along the way. Although intelligence and knowledge are closely linked, they're not the same thing. You could essentially teach an imbecile the same things you could teach a genius, it would just take a hell of a lot longer.
I use this difference in order to argue away any doubts of my intelligence. I really am passably intelligent, I'm just bugger-all in regards to knowledge.
And you've got to admit, I've got to be at least a little clever in order to pull that one off.