Language of love pursuing hearts in days gone by (6)
I believe the answer is:
pashto
'language' is the definition.
(Pashto is an example)
'love pursuing hearts in days gone by' is the wordplay.
'love' becomes 'o' (love means zero in tennis).
'pursuing' is a charade indicator (letters next to each other).
'hearts' becomes 'h' (abbreviation used in card games e.g. bridge).
'in' is an insertion indicator.
'days gone by' becomes 'past' (I've seen this in another clue).
'h' placed into 'past' is 'pasht'.
'o' put after 'pasht' is 'PASHTO'.
'of' is the link.
(Other definitions for pashto that I've seen before include "hear this from Afghanistan" , "Afghan" , "language follows!" , "Iranian language spoken in Afghanistan and Pakistan" .)