Arabic, Urdu and Farsi are written from right to left. These are the languages I know; there may well be others.
Native speakers of these languages might face the following challenges: difficulty reading the letters of written English; difficulty adapting to a new way of writing; difficulty remembering words at a low level because they can't revise using the written word. It's a good idea to represent the words phonetically in their own language until students are familiar with the new alphabet.
Having said that many speakers of these languages have excellent command of the alphabet used in English. For example, Arabic speakers throughout North Africa have French as a second language; this means that they can read easily written English words.
All the best,