Just like all of our hair is different, all vendor hair is different. The main difference in these textures are coarseness/heaviness. Where virgin unprocessed hair is the "lightest"/least coarse" and kinky straight/italian yaky is the "heaviest"/most coarse.
-Light yaky is kinda like diet yaky lol. its really really lightly processed but is still very silky. Doesnt need flat ironing to be straight, usually holds a curl well. Its silky and has sheen, not shine like beauty supply store hair or synthetic hair.
-Yaky is just the medium. It's processed more than light yaky, less than italian yaky/coarse yaky/kinky straight. Less sheen than light yaky, less coarse/textured than coarse yaky.
-Here's where things get tricky. . . back in the day, there was coarse yaky which was still straight, but had "texture" and coarseness but didn't swell like italian yaky or kinky staight. Now because of vendors like kinkycurlyyaki.com, folks have started using "coarse yaky" interchangeably with italian yaky/kinky straight. But again, you have to get pictures to/from your vendor. the name "coarse yaky" means different things to different vendors.
-Italian yaky is usually heavily textured but still flat irons well. Much of the italian yaky, ive experienced has Folks usually have to look for the uniform fake looking "crimps" that vendors use to texture hair. Italian yaky, may or may not swell, its usually dependent on the vendor. It is supposed to resemble pressed out fine, natural hair. Italian yaky tends to flat iron to yaky meaning, to me at least, italian yaky is more of a "curl pattern" than a texture with a unique coarseness.
-Kinky straight, in my experience usually looks like a more processed italian yaky. The washed or unflat ironed kinky straight, looks like italian yaky. Ive found depending on the vendor, kinky straight is usually a little harder to maintain because of the extra processing. It's prone to swelling and tangling. BUT if you get a good vendor/batch, it's pretty much heaven because for me, with my natural 4a/4b hair, dark skin, and round face, its the most realistic looking straight hair. kinky straight in its natural state is supposed to resemble pressed out natural hair. For some vendors, they have either italian yaky, coarse yaky OR kinky straight but not all three so they may use the names interchangeably. . . just get pictures and ask questions. You are paying them to provide both a good AND a service. Girl get your money's worth.
As far as indian and chinese, those are supposed to be the origins of the hair. I dont think it actually comes from a person in india or a person from china, just a different moose or yak. lol. I dont mind, I think I prefer my weave from an animal and not a stranger. But indian hair is the cheapest, most readily available. Its prone to tangling, but its still better than most of whats in the beauty supply store. Chinese hair is heavier, denser. As in the individual strands are thicker and denser. Ive found that it takes much more heat to curl chinese hair, and it sometimes doesnt hold a curl. It would just rather be straight. lol. But I have found that if I want a curly style, like a kinky curl unit, chinese is the way to go. The processed curls hold better than ones I would add with a curling iron. Just a sidenote, I prefer malaysian (or whatever the vendor offers that isnt indian or chinese) for my straight units. Because I want something less prone to tangling than indian but will actually curl & hold a curl unlike ome chinese hair.
Hope that helps hon.