Most of the places in Tamilnadu I've heard refer to the term "Superfast" as "ativega viraivu vandi". Coimbatore, Chennai Central, Chennai Egmore, most of Coimbatore - Katpadi Line. When there is a word in the language, the announcements should ideally use that word instead of the English term. Isn't that the beauty of local languages? It is obviously not mandatory but such a word does exists and it can be implemented on the lines of promoting the language in a way.