Some people naturally find spelling easy. They have what is know as a photographic memory for written words. When they see a word written they are impressed not only with its meaning but with its very shape. They see it in their minds’ eye.
Although some professionals believe that photographic memory is a myth, there has also been evidence to show that photographic memory is a real phenomenon. A woman who was studied by Charles Stromeyer was capable of remembering poetry that had been written in a different language. Photographic memory is a rare element that is found in less than 10% of the population.
Other people just as naturally have no visual or photographic memory of this sort, although they may have a wonderful memory for the sound of a spoken word and perhaps quick and fine perception of a word’s inner meaning. To such people spelling errors will be all too easy.
Dyslexia is a learning disability that mainly affects reading and spelling. Common features of English dyslexia include spelling errors (‘nock’ for ‘knock’; ‘jerney’ for ‘journey’); mixing upper and lowercase letters in writing (for example: ‘numBers’), and confusing letters like ‘b’ and ‘d’.
At my hand, A Parents’ Guide To Dyslexia, Dyspraxia And Other Leaning Difficulties, by Dr Valerie Muter and Dr Helen Likierman, the authors point out that children with Dyslexia have problem with an aspect of spoken language know as phonological processing, which means that children find it hard to make sense of the speech sounds in words, they just can’t easily break a spoken word like ‘stop’ into ints separate sounds ‘s’ – ‘t’ – ‘o’ -‘p’. Nor can they easily put sounds together, or blending. 
But this doesn’t make sense to Chinese language, because the phonological rules don’t apply to Chinese written language, and to read Chinese does not require analysis into phonemes. Because all Chinese letters are either pictograms or ideograms, although most of Chinese characters are phonograms, which are compounds of radicals, half of it represents meaning and another half represents sound. It’s no doubt that Chinese people also have dyslexia, or reading difficulties. The only reasonable explanation of the cause of Chinese dyslexia can not be phonological processing problems. Chinese Dyslexia might be caused by the poor photographic memory, or a kind of deficiency of photographic memory, this can also apply to some subtypes of English dyslexia, mentioned above.
During the historical evolution, actually English language has developed into a most unkind language. So many of its words are not written at all as they are spoken. So many of its letters are silent, so many have sounds that vary from one word to another, and there are so many rules continually broken, that unless you have a strong photographic memory you are almost certain to make some spelling errors in English.
For instance, very often double consonants have the same sound as a single consonant. gh may have the same sound as g (ghastly), or c as ch (chaos), or t as th (thyme). The famous double consonant, ph is pronounced neither like a p nor an h, but like an f (Phyllis). The kind of double consonant that gives most trouble should perhaps be called the twin consonant, bitten, pepper. These words required a strong visual memory.
In this interesting case, Dyslexia has a language barrier reported by Guardian, the Japanese child, whose parents are English, but he was born and grew up in Japan, was severely dyslexic, but only in one language. In the other, he was probably in the top 10% of readers of his age. A study into this case, led by Li Hai Tan tells us about how dyslexia affects the brain, and how brain functioning may cause he dyslexia. Readers of Chinese use different parts of the brain from readers of English. 
Dyslexia in different language may have totally different cause, English, French and Italian dyslexics may be caused by phonemic analysis, while Chinese, Japanese dyslexics by photographic memory and analysis.