Some clarification.
There are two types of dyslexia, Developmental Dyslexia and Alexia (acquired dyslexia)
Most children have Developmental Dyslexia, which has a genetic origin, inherited from at least one biological parent
Dyslexia is a reading disability.
Dyslexia is about having problems with a man made communication system the visual notation of speech, or having problems decoding the graphic symbols used to represent the sounds of speech.
Dyslexia is language dependent. There are many different writing systems developed by different cultures around the world, and each writing system requires slightly different cognitive skill sets to decode the different types of graphic symbols used or the different writing system orthographies.
The purest writing systems are the logographic systems writing systems such as Chinese and Japanese, which have a single sound to single symbol relationship. And the most complex writing systems are the alphabets, such as the Latin alphabet we use.
There are many more different writing systems used in Asia, Africa and the Middle East.
Each writing system requires a slightly different cognitive skill set to decode and recode the symbols used to represent the sounds of speech. Which in turn means that there are different cognitive deficits which will cause the dyslexic symptom, of having problems decoding the graphic symbols that make up a writing system.
Next within each writing system there are the every day languages which use the writing systems symbols. English is part of the Latin Alphabet writing system, which is primarily used in Western Europe and North America.
The truest, Shallowest Orthographies, in the Latin Alphabet System are Italian and Finnish, the Deepest Orthography or most complex language is English.
S
o Dyslexia is language dependent, and the underlying cognitive deficit or information processing disorder which cause the dyslexic symptom may vary from one writing system to another.
Much of the early dyslexia research focused on the problems of the Latin Alphabet system used in Europe, at the end of the the Nineteenth Century, and English especially in the USA during the Twentieth Century. More recently there has been a great deal of research coming from China as they become more dependent on the use of the visual notation of speech as the main form of communication.
There a few isolated societies who do not have dyslexia, where they do not use a writing system as a form of communication.
There are three cognitive subtypes of dyslexia auditory, visual, and attentional. Which have been the focus of international research over the last decade or so.
So auditory processing (Listening) problems, visual processing problems, attention problems or any combination of the three are the underlying causes of the dyslexic symptom.