Composer somewhere in Germany briefly joins Australian (7)
I believe the answer is:
berlioz
'composer' is the definition.
(I've seen this before)
'somewhere in germany briefly joins australian' is the wordplay.
'somewhere in germany' becomes 'Berlin' (Berlin is the capital of Germany).
'briefly' means to remove the last letter.
'joins' is a charade indicator (letters next to each other).
'australian' becomes 'Oz' (nickname for Australia).
'berlin' with its last letter taken off is 'berli'.
'berli'+'oz'='BERLIOZ'
(Other definitions for berlioz that I've seen before include "French composer, d. 1869" , "Trojans composer" , "Barman" , "Composer of The Damnation of Faust, d. 1869" , "Symphonie fantastique composer, d. 1869" .)