Dialect of festival director from the south (7)
I believe the answer is:
geordie
'dialect' is the definition.
(I've seen this before)
'festival director from the south' is the wordplay.
'festival' becomes 'eid' (Muslim festival).
'director' becomes 'roeg' (I've seen this before).
'from the south' is a reversal indicator (in a down clue, letters go up).
'eid'+'roeg'='eidroeg'
'eidroeg' reversed gives 'GEORDIE'.
'of' is the link.
(Other definitions for geordie that I've seen before include "Native of Tyneside" , "Newcastle-upon-Tyne native" , "Tynesider" , "North-easterner" , "Newcastle person" .)