Indonesian island adopting English language (7)
I believe the answer is:
bengali
'language' is the definition.
(I've seen this before)
'indonesian island adopting english' is the wordplay.
'indonesian island' becomes 'bali' (island of Indonesia).
'adopting' indicates putting letters inside (inserted letters are taken on or adopted).
'english' becomes 'eng' (abbreviation).
'bali' going around 'eng' is 'BENGALI'.
(Other definitions for bengali that I've seen before include "Subcontinental" , "Language of Bangladesh and northeast India" , "Native of Calcutta region" , "may be Indian" , "East Indian" .)