Sequestering an island with no language guide (9)
I believe the answer is:
isolating
'sequestering' is the definition.
('isolate' can be a synonym of 'sequester')
'an island with no language guide' is the wordplay.
'an island' becomes 'i'.
'with' is an insertion indicator.
'no' becomes 'O' (O resembles 0).
'language guide' becomes 'slating' (I am not sure about this - if you are sure you should believe this answer much more).
'o' put inside 'slating' is 'solating'.
'i'+'solating'='ISOLATING'
Can you help me to learn more?
(Other definitions for isolating that I've seen before include "maintaining detachment?" , "Ligations (anag.)" , "Detaching, separating" .)