Join the English diplomat (7)
I believe the answer is:
attache
'diplomat' is the definition.
(I've seen this before)
'join the english' is the wordplay.
'join' becomes 'attach' (attaching is a kind of joining).
'the english' becomes 'e' (abbreviation).
'attach'+'e'='ATTACHE'
(Other definitions for attache that I've seen before include "Ambassador's aide" , "This case is for carrying documents" , "Member of ambassador's staff" , "Embassy member" , "Connected to the French" .)