Siren of traditional tales on the French island (7)
I believe the answer is:
lorelei
'siren' is the definition.
(I know that Lorelei is a siren)
'traditional tales on the french island' is the wordplay.
'traditional tales' becomes 'lore' (I've seen this in another clue).
'on' says to put letters next to each other (in a down clue, letters appear on others).
'the french' becomes 'le' ('the' in French).
'island' becomes 'i' (geographical abbreviation).
'lore'+'le'+'i'='LORELEI'
'of' acts as a link.
(Other definitions for lorelei that I've seen before include "High rock in the Rhine gorge" , "Rhine rock famed for siren" , "Great Rock on the Rhine where sirens lived in legend" , "voice to die for" , "Famous Rhine rock" .)