Iggi- if your job is to teach literacy (that is the job of every teacher whatever subject they teach) and role-model good spoken and written English at work, how can you do that job if you can't do those things?
You can't teach driving if you can't drive. You can't teach a foreign language without being able to write, speak and read it. You can't be a chef unless you can cook. Why do you think you can be a teacher if you can not do the things you need to be able to do to teach?
It is not about disability discrimination. It is about having the skills to do the job.
If you are dyslexic to the point where you can not spell, compose accurate sentences, use grammar appropriately - how can you teach children to do so? There may be jobs where dyslexia is no issue whatsoever, teaching is not one of them if the dyslexia is that bad.
We have been put in a postion in my school where a teacher did not declare they were dyslexic although they knew. They had attended a private school where their English results had been 'helped along' by a teacher, at university their course was mainly practical and involved Technology, Science and Maths, they had almost failed their teacher training (they later admitted to us) until their partner began planning lessons for them.
When they started teaching with us they could not cope. Their written English was awful. They could not mark books accurately. They could not plan lessons or manage the work load (because their dyslexia affected their organisational skills). Their classroom was chaotic because they were so disorganised. Eventually, our SENCO said she thought they were dyslexic and they admitted it.
Their union asked us to give them a 40% timetable to accomodate this but pay them as if they were a full-time teacher. We refused and they took legal advice. As they had been asked in the interview if there was anything they had not told us about that might in any way affect their ability to do the job or that we might be able to make adjusments for to help them do the job and they had replied no, the legal advice was they had misled us. They resigned.
Lovely person, not suitable for teaching in a school. Runs a scuba diving company in Australia now.