Twin, one with incoherent dialect found around north (9)
I believe the answer is:
identical
'twin' is the definition.
(identical twin is a kind of twin)
'one with incoherent dialect found around north' is the wordplay.
I cannot really see how this works, but
'one' could be 'i' (Roman numeral) and 'i' is found in the answer.
'around' could be 'ca' (circa) and 'ca' is found in the answer.
'north' could be 'n' ('N' can be a synonym of 'north') and 'n' is found within the answer.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for identical that I've seen before include "Equal" , "uniform" , "Matching" , "Not any different" , "showing no change" .)