To be registered as a health practitioner in NZ you must be able to demonstrate that your English language skills will enable you to safely practice your profession. If you’ve taken your original medical diploma in English, then you don’t need to take a language test. If not, then you will need to prove otherwise.
If you are currently practising in a non-English country then it’s likely you’ll need to sit an English exam such as IELTS / OET. If you’re working in the UK but completed your Medical training elsewhere then you may be able to meet the English language policy via references. You can click here for further info for the English Language policy for NZ