Twin brother in Berlin agreed to meet Swan (5)
I believe the answer is:
jacob
'twin brother in berlin' is the definition.
'jacob' can be an answer for 'twin' (I have seen 'Twin of Esau ' mean 'jacob' so perhaps 'twin' could also mean 'jacob'). I'm not sure about the 'brother in berlin' bit.
'agreed to meet swan' is the wordplay.
'agreed to' becomes 'ja' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'meet' means one lot of letters go next to another.
'swan' becomes 'cob' (cob is a kind of swan).
'ja'+'cob'='JACOB'
Can you help me to learn more?
(Other definitions for jacob that I've seen before include "Rachel's husband" , "man" , "Hebrew patriarch" , "Biblical son of Isaac" , "Twin of Esau" .)