its not the matter of writing from other side, as per the Rule Regional is written in that language from where it Belong irrespective of source/destination.
For Example Train no 12505/12506 belong to NFR so its Regional name is written in Assamese as it source station is Assam. Now take another Example Train 14055/14056 belong to NR so its Regional name is written in Urdu as its source station is Delhi.
Regional name is Fixed for both the side following the Rule