Reticent engaging with German forger? (6)
I believe the answer is:
smithy
'forger?' is the definition.
(blacksmith)
'reticent engaging with german' is the wordplay.
'reticent' becomes 'shy' (both can mean withdrawn or timid).
'engaging' means one lot of letters goes inside another.
'with german' becomes 'mit' ('with' in German).
'shy' enclosing 'mit' is 'SMITHY'.
(Other definitions for smithy that I've seen before include "Blacksmith's forge" , "Old forge" , "work area" , "Workplace for forging metal" , "Vulcan was concerned?" .)