I would finally leave after the German mock (6)
I believe the answer is:
'mock' is the definition.
(deriding is a kind of mocking)
'i would finally leave after the german' is the wordplay.
'i would' becomes 'I'd'.
'finally' suggests the final letters.
'after' is a charade indicator (letters next to each other).
'the german' becomes 'der' ('the' in German).
The final letter of 'leave' is 'e'.
'ide' put after 'der' is 'DERIDE'.
(Other definitions for deride that I've seen before include "Ridicule, scoff at" , "Ridicule, laugh at" , "Mock and jeer" , "Knock" , "Mock, scorn" .)