This question was put on hold as 'not clear' but OP has said 'subcontinental languages' which obviously refers to Indian subcontinental languages, because I have not heard of any other subcontinent. Moreover the tag 'Indian English' has been used.
My guess is that this is merely used to express a plural form (...) Am I right?
OP wants to know 'whether I am is right to think that double words like big big and small small indicate plurality?' The title asks: How should I express this in (idiomatically correct) English?
What is not clear in this question?
John Hamilton has written a very confident, correct answer that was supported by 1006a. It says that OP is right to interpret plurality, and the equivalent English term would be 'numerous' or 'many.' I can confirm that this answer is correct, and I ought to know because I am Indian!
MANY USERS MADE WELL-INTENTIONED SPECULATIVE ANSWERS THAT WERE FAR OFF TARGET.
Are we supposed to present 'educated guesswork' as answers rather than comments? Was that the reason for putting this Q on hold?
If not, then there is nothing ambiguous about the question and it ought to be reopened.