I live in southern India, and for a long time I've been curious about this phenomenon that I've observed.
Indian English uses the word "only" in a special way. It's used to emphasize things. Sort of like US/UK/AU/NZ people would use the word "indeed."
Some examples (several of which shamelessly stolen from this answer):
I was born in Calcutta only.
You're just stating clearly where you were born.
It's a new movie only.
You're not suggesting anything with the word "only". You're just confirming that the movie is definitely new.
It's on that branch only.
Again, you're sure and you're stating it clearly.
They are Punjabi only.
He is a garbage collector only.
This is not necessarily meant to be offensive, as in UK/US/AU English "He's only a garbage collector." Rather, the speaker is stating what someone's job is, unambigiously.
He paid me 5000 Rupees only.
You're not trying to imply that the amount is too low or insufficient, as in "He paid me only 5000 Rupees." You're saying it was exactly 5000 Rupees, and emphasizing that you recall the matter clearly and are sure.
We went to the beach only.
Nothing negative about the beach. That's simply where you went, and you want to state that clearly.
- Excuse me, I have a parcel for Mr. Kumar.
- That's me only.
Kumar is confirming that he is indeed the person they are looking for.
What is the origin of this usage of "only"?
I certainly don't recognize it from US/UK/AU/NZ English. I know that many unique features of Indian English are actually old features of British English that have since died out elsewhere but remain in India. Is that the case here?
Another theory I have is that it developed as a means to substitute a feature of certain Indian languages. For example, in Hindi, people say "hee" at the end of sentences all the time, for the sake of emphasis. Similarly, in Tamil (which I partly know), they say "tha" at the end. It has exactly that function. For example, "Athu tha" means "That, indeed." So another possible theory is that this usage of "only" developed as speakers felt the need to have such an intensifier at the end of sentences, as many Indian languages do. Without it they may have felt that the sentence would lack credibility or sincerity.
Does anyone have any insights, research or knowledge about the origins of this usage of "only"?