According to the Japan Dyslexia Society NPO-Edge:

“In Japan dyslexia is considered as one of main symptoms of LD (learning disabilities)”.

The notion of LD “is still confused,” although the Ministry of Health and Welfare and the Ministry of Education formulated a first definition in 1997 and 1999.

“Symptoms such as ADHD, autism, and [being] mentally retarded” were included as being in the “learning disabilities” bracket, according to the Japanese Academy of Learning Disabilities.

The word dyslexia in Japan is used purely for acquired dyslexia in medical terminology. In educational terms, “LD is widely used in Japan”. The definition for this is defined by the Ministry of Education and Ministry of Health & Welfare to include dyslexia, dysgraphia, and dyscalculia.

The Japanese authorities try to use the term “developmental dyslexia” to differentiate from dyslexia which is caused by accident or illness and learning disabilities, which in Japan still sometimes includes “retarded, autism, ADHD and epilepsy”.

DSM-III (American criteria) and ICD-10 (World Health Organisation criteria) are well known amongst medical practitioners and psychologists. Reading, writing and calculation difficulties are listed as Learning Disorders but are actually rarely diagnosed as such in medical institutions as there are no criteria for diagnosis.

Furthermore, ADHD and autism are currently attracting more attention which could be another reason for not having children being diagnosed as being dyslexic.

There is some confusion in Japan about the term dyslexia, and the meaning of the term. For instance, in 2007, one survey polled teachers to test their knowledge of dyslexia. The results were that 68% of the respondents had not heard of the word dyslexia. Of the 31% who had heard of it (1% did not respond), 45% did not understand what it meant.

A comparative study was published showing different results from different research. This showed conflicting results over time:

Japanese Language Education and Dyslexia:
On the Necessity of the Dyslexia Research

Research by Sandra Tanahashi suggests:

>> A basic definition is surprisingly difficult to find for the term dyslexia. This seems to be because the term itself can be used to describe any number of LD that involve difficulty in decoding writing. Also, several forms of dyslexia have been identified. [Note] that the word dyslexia is referring to developmental dyslexia—a condition a child is born with, not acquired dyslexia, which is caused by a trauma to the brain. Experts do agree on several points regarding dyslexia. It is neurological in origin.

>> Dyslexics use a different part of their brain for language processing than non-dyslexics. It is a permanent condition, but problems can be ameliorated with proper training. It is often accompanied by poor short-term memory. The final point on which the experts agree is that dyslexia most commonly manifests itself as a difficulty with accurate and / or fluent word recognition and with poor spelling and decoding abilities. […] Dyslexia is “a difficulty in reading in people who have the intelligence, motivation, and education necessary for successful reading.” (p. 2860) <<

The Japan Dyslexia Association gives the following information:

>> First, when we talk about definitions and situations, we have to use the word “disability”. Traditionally, in the medical field, things that do not work are customarily described as “disability”. An example would be, “Fracture left a defect in the elbow joint.” <<

They go on to say:

>> The word “disability” may be a bad word. Since the notation “harm” does not cause harm, it is becoming increasingly common to write “gai”. “Disability” is a translation of English word “disorder”, which means minor illness or illness, and impairment means “damage”. In this way, we don’t have the proper Japanese, so we use the customary expression “disability” here. We’ll change it as soon as you […]understand it. <<
(translation provided by Google, original available online at jdyslexia.com)

They continue:

>> The dyslexia covered by this association usually refers to a state in which conversation (understanding and expression of spoken language) can be performed normally, and intellectually within the standard range, but the processing (reading and writing) of textual information does not go well.

>> In childhood, they tend to be uninterested in letters or like to read picture books but not try to read them on their own. In school, the students are unable to remember the letters, continue to read in a jarring way, often skip reading and reading on their own, and show situations where it is difficult to read and understand from the letters, although they can be understood by speaking. It is not impossible to read at all, and the reading speed is very slow and there are many mistakes. (E.g., clogging sounds or sounds that stretch like “ko” or “you”) Also, with Kanji, reading and writing differ depending on the next character, making reading and writing difficult.

>> In the upper grades, there are more types of kanji, more difficult words, longer sentences, and the amount of sentences to read is no longer odd. Also, unlike the Japanese alphabet, many words have many sounds and the letters and sounds do not match, so it becomes very difficult to read if you learn English. They may find it hard to work, and because they are lazy because of their intellectual abilities, they can become stiff and lethargic. In addition, texts that you see for the first time are difficult to read and difficult to write. <<

However, the Japanese Dyslexia Association states that it uses the International Dyslexia Association definition of dyslexia. As the IDA focuses on phonological fluency, it’s hardly surprising that a child’s dyslexia won’t generally be picked up unless that child is also reading and writing in an alphabetic language.

The following study gives some credibility to this view:

In October 2002, the Japanese Ministry of Education undertook a comprehensive survey on the incidence of dyslexia and other learning difficulties, announcing that there could be 6.3% incidence of children in the ordinary elementary schools having severe difficulties in learning despite of their level of intelligence.

Unfortunately the survey was based on questionnaires which were answered by classroom teachers who are not greatly aware of dyslexia or other learning difficulties.

See for instance:
>>Gifu University Faculty of Education Research Report, Vol. 56, No.1