Testimony of French accepted by English fellow (8)
I believe the answer is:
evidence
'testimony' is the definition.
(testimony is evidence given in court)
'of french accepted by english fellow' is the wordplay.
'of french' becomes 'de' ('of' in French).
'accepted by' is an insertion indicator (inserted letters are accepted).
'english' becomes 'e' (abbreviation).
'fellow' becomes 'Vince' (man's name).
'e'+'vince'='evince'
'de' put into 'evince' is 'EVIDENCE'.
(Other definitions for evidence that I've seen before include "support" , "Indication" , "Facts on which to establish verdict" , "Information to help form a conclusion" , "Information in a law case" .)