I don't understand your question.
Why is Writing in Arabic a problem?
Where/how are you downloading InDesign 2020?
Why is your OS language set to Arabic if you don't read/write in that language?
You would need to download the Arabic version of InDesign, using Creative Cloud. Go though the discussion below it will help you
Also see the following
Now it's working 🙂 thanks a lot. Thank you very much