New Zealand is an English-speaking country, so there is no need to learn any other language. The Maori language, Te Reo, is also used in some heavily Maori areas and is offered as an option in schools.
To obtain a residency visa, you must prove that you have a good level of English and may be required to take an English exam.
If you would like to improve your business English, or have a family member who would like to take English classes, the following schools have different levels of classes:
CCEL AUCKLAND - http://www.ccel.co.nz/ccel-auckland.php
Level 7, 155 Queen St, PO Box 7206, Auckland 1141, New Zealand
Phone +64 9 379 8710, Fax +64 9 379 8713
Languages International - http://www.languages.ac.nz
PO Box 5293 Auckland, New Zealand 1036 (Two locations in Auckland)
Phone +64 9 309-0615, Fax +64 9 377-2806
UUNZ Business Institute - http://www.uunz.ac.nz
100 Symonds Street, Auckland CBD, New Zealand
Phone +64 9 915 3390, Fax +64 9 915 3399