Once I read that left-handers tend to be more skilled than right-handers because there are some tasks which can only be done with the right hand, such as driving (unless you live in England) or opening a can. So they have to develop some ability with the other hand, thus stimulating both sides of their brain, while right handers don't need to do it, what would give left handers a mental advantage. Stimulation is a key to mental development, but there are many other ways of stimulating a child's brain, I don't think this is determinant. By the way, I'm a left hander.
I am left handed and many people tell me that I have a "gift" for languages. I seem to have a brain for linguistics.
My right-handed sister is slow at learning languages. (nothing against her, I love my sister!) I've been trying to teach her Spanish, but she's slowly making progress. I can say that there is a big linguistic difference between us. Maybe it has to do with our brain hemispheres?