Unleash tirade as the French blunder (3,3)
I believe the answer is:
let rip
'unleash tirade' is the definition.
(to let rip is to rant)
'the french blunder' is the wordplay.
'the french' becomes 'le'.
'blunder' becomes 'trip' (trip is a kind of blunder).
'le'+'trip'='LET RIP'
'as' is the link.
(Other definitions for let rip that I've seen before include "Act unrestrainedly" , "Triple (anag)" , "Talk aggressively" , "Behave without restraint" , "Sound off" .)