Joke made by judge is French (4)
I believe the answer is:
jest
'joke' is the definition.
(synonyms)
'by judge is french' is the wordplay.
'by' means one lot of letters go next to another.
'judge' becomes 'j' (abbreviation for judge).
'is french' becomes 'est' (I've seen this in other clues).
'j'+'est' is 'JEST'.
'made' is the link.
(Other definitions for jest that I've seen before include "` `Many a true word is spoken in . . . .' '" , "Joke, fool about" , "Piece of humour" , "Witty remark" , "Ridicule" .)