Hello Rob,
Geoffrey P. Oldham's book "Badges and Insignia of the New Zealand Army, New and Revised 2nd Edition, 2011", lists a similar looking badge on page 99.
Chapter 10. Miscellaneous New Zealand Badges
Badges of Appointment and Qualification Badges
10/81. Interpreter
I hope your able to track down more information about your interpreter badge
Cheers,
Invest