I'm soooooo insecure about my intelligence

You sound a lot like my first girlfriend. She was very passionate about learning and went mental, whenever she failed at something.

First, get off webMD, or any other website that tries to convince you, that you got some disease. 95% says you don't.

Also grades are garbage... A bunch of numbers given to you for conforming to an outdated system. Everyone is good at something and schools should encourage students to get better at their strengths, not hold them back because of their flaws.

I know a guy who only finished high school and never got a degree. Dude makes twice the money I make and I got a degree in economics.
I know a girl with 2 degrees, grade-A student, perfect scores. She makes a third of what I make.
I sell cars, have a small business and a Saturday job.

Not everybody is cut out to be a professor. I found lots of stuff in university boring, tedious, or simply too demanding and had my fair share of cheating.
Seeking knowledge is a very good thing, but there is no reason to beat yourself over it. Nobody said it was gonna be easy. The important thing is that you have a passion and are working towards achieving it.

Believe me, I've had my fair share of self hate, self doubt, depression, etc for not making it big before the age of 25. Got a big reality slap in the face about 2 years ago, but that doesn't stop me. I'm not giving up on the dream of retiring on a yacht. I'm doing that shit.

PS: Chinese and Japanese are very difficult languages. Everything is completely different.

I'm Bulgarian and learning English was easy for me. Everything is in English, starting from movies, all the way to warning labels on bathroom air fresheners (cause they are so dangerous), so you learn, even if you're not trying your best. If you asked me about grammar rules in the English language, I'll look like an idiot, but at the same time, I can pull off a smooth American accent and speak properly.
Learning German was ok too, since in a few ways it's similar to English. Grammar there was a bitch and you need to learn it copy-paste style.
Learning Spanish was far more difficult and I never learned it properly.

But if I had to learn Japanese, forget about it. No chance of me learning that stuff. So already I can tell you you are better at learning languages than me.
Because you chose on of the hardest languages and dived head first into the language of the rising sun, drifting, samurais and vtec.

So don't be too hard on yourself, take a deep breath, take a break, relax, do stuff you like and keep soldiering on.

talk way too much

Megadriver gave some great advice.
Just based on your post you arent as poor at grammar as you think.
It would be easy to say maybe you have one of these popular learning issues.
I.E. add, adhd, hdtv, ass burgers, etc.
But Im not a big fan of labeling and medicating anyone who doesnt fit the cookie cutter mold.
People learn differently and have different skills.
Embrace your strengths.
As for kids.
The world has enough.

"If I write anything, I always have to explain myself because it's incoherent and I don't have the innate ability to reason logically (not to mention a weak grasp of grammar, especially in other languages)."

It would have been easier to read your post if you'd whacked the carriage return key a few times, and you wrote "conquest" when you obviously meant "quest", but the vocabulary, grammar, punctuation and structure of your post makes it clear you are definitely not an idiot when it comes to writing English. That calls into question everything else negative you say about yourself.

It sounds like you're flailing around somewhere in the education system. Not everybody copes well in academic settings, but that doesn't mean they're stupid, useless and will never amount to anything. All school, from kindergarten to post-grad, is a matter of following the programme and jumping through a progression of hoops. Being bad at that may seem a curse at the moment, but in reality it isn't.

At the worst, being bad at school means it would probably be unwise for you to seek a career in teaching where you would spend your life trying to pound other square pegs into round holes and being required to reward the good little parrots who repeat exactly what they've been taught. At the best, it could mean that your brain doesn't work the way those of others do, and you could find a place in the world where a skewed, original approach is a valuable asset.

You seem to have spent a lot of time working on a long list of all the things you're less than perfect at, but there must be something you enjoy and do well. Maybe you're depressed and incapable of assessing your abilities rationally right now, but I think you should focus on finding something you're good at and becoming truly engaged with it.

but the thing is are you sexy? just wonderin it might not be as bad as you think if you cute. its pretty damn bad if you ugly as a motherfucker. im just tryna tap...

You could take an IQ test. Honestly, it's a risk because it could come back with a poor result, but given how much this is fucking with you it might be worth it just to get some possible positive affirmation.