"do the needful", "please revert back to me"-- phrases like these are not 'invented' by some Indian speakers. These are the stuff Indian savants picked up from the old English books. Then, these savants taught this stuff to fellow Indians and this dynamic gets reproduced everyday.
See an entry from Charles Scholl, Geroge Mcaulaly et al's "A Phraseological Dictionary of Commercial Correspondence in the English, German, French & Spanish Languages, with an Appendix Containing Lists of Commercial Abbreviations, Geographical Names, the Principal Articles of Commerce", published in 1891:
"Needful: he will do what is needful under the circumstances. We rely on your doing the needful for the protection of our interests. With which will you please do the needful. With which we shall do the needful, and credit you for the amount in due course. I shall do the needful at maturity. I enclose draft for 100 pounds at two months, to which I will thank you to do the needful"
Another entry from a law journal published in 1833 in UK: "The letter was immediately given by the bankrupt to the defendant, with directions that as the voyage was altered, he, the defendant, would do the needful."
It's interesting to see where it came from, but why does it persist? Is consuming English language media and the largest internet sites uncommon for English speaking people in India? I imagine I'd notice pretty quickly that English speakers in TV, movies, and on youtube, don't speak the way they did in the 1800s.
So, India inherited the British civil services system wholesale. The formal pseudo legal language used in the system, instituted by the British, continued. It was different enough from the language taught in schools that when someone was exposed to it or had to use it tried to conform to it's idiosyncrasies.
Over time, isolated from the cultural changes happening to the English world, it developed in it's own way. Like the albino and blind animals evolved in the seclusion of an isolated cave system.
Today, the best way to observe this secluded language branch is to read official Indian government announcements.
It has started to meld back into the main branch [0][1] as younger and younger, more exposed to the global English culture, take over responsibilities.
See an entry from Charles Scholl, Geroge Mcaulaly et al's "A Phraseological Dictionary of Commercial Correspondence in the English, German, French & Spanish Languages, with an Appendix Containing Lists of Commercial Abbreviations, Geographical Names, the Principal Articles of Commerce", published in 1891:
"Needful: he will do what is needful under the circumstances. We rely on your doing the needful for the protection of our interests. With which will you please do the needful. With which we shall do the needful, and credit you for the amount in due course. I shall do the needful at maturity. I enclose draft for 100 pounds at two months, to which I will thank you to do the needful"
Another entry from a law journal published in 1833 in UK: "The letter was immediately given by the bankrupt to the defendant, with directions that as the voyage was altered, he, the defendant, would do the needful."