In here, a German is keen (5)
I believe the answer is:
eager
'is keen' is the definition.
(I've seen this in another clue)
'in here a german' is the wordplay.
'in' says the answer is hidden in the clue.
'EAGER' can be found hidden inside 'here a german'.
(Other definitions for eager that I've seen before include "really keen" , "Alert and active type?" , "Enthusiastic, raring to go" , "Thirsty" , "passionate" .)