A leader in technology to teach foreign diplomat (7)
I believe the answer is:
attache
'diplomat' is the definition.
(I've seen this before)
'a leader in technology to teach foreign' is the wordplay.
'leader in' suggests taking the first letters.
'foreign' is an anagram indicator (foreign order of the letters).
The initial letter of 'technology' is 't'.
'teach' anagrammed gives 'tache'.
'a'+'t'+'tache'='ATTACHE'
(Other definitions for attache that I've seen before include "Ambassador's aide" , "Junior official" , "That ace (anag.)" , "Member of ambassador's staff" , "Briefcase or member of a diplomatic mission" .)