The stronghold of a different dialect (7)
I believe the answer is:
citadel
'the stronghold' is the definition.
(citadel is a kind of stronghold)
'a different dialect' is the wordplay.
'a different' is an anagram indicator.
'dialect' is an anagram of 'CITADEL'.
'of' is the link.
(Other definitions for citadel that I've seen before include "Urban stronghold - dialect (anag)" , "Urban fortress" , "Highly-secure building" , "Stronghold (of the Salvation Army?)" , "Bastion" .)