Somewhere in Germany, Italian turns a large key (9)
I believe the answer is:
essential
'key' is the definition.
(I've seen this before)
'somewhere in germany italian turns a large' is the wordplay.
'somewhere in germany' becomes 'essen' (I can't justify this - if you can you should give a lot more credence to this answer).
'italian' becomes 'it' (abbreviation for Italian).
'turns' is a reversal indicator.
'large' becomes 'L' (eg in clothes sizes).
'it' reversed gives 'ti'.
'essen'+'ti'+'a'+'l'='ESSENTIAL'
Can you help me to learn more?
(Other definitions for essential that I've seen before include "Basic or necessary" , "Type of oil" , "organic" , "Vitally important" , "absolutely neccessary?" .)