He learned te reo Maori after a stint teaching English as a second language in Bangladesh.
"While I did learn te reo Maori as an adult, I have and will always be shaped by that lack of opportunity when I was young and that's what I want to change for others.
"Learning a new language as an adult is often a challenge and that was the case here as well.
"So, even years later, my receptive understanding of te reo Maori is much better than my speaking ability.
"That is also often a consequence of growing up in a monolingual environment."
Growing up bilingual or multilingual is an advantage which 75 to 80 per cent of people in the world had, he added.
"Those who can only speak one language (even if it is English) are immediately at a disadvantage compared with others who are able to use a number of languages in different contexts, with different people, and for different purposes."
Te reo Maori should be the first choice for a second language, May said.
"We need to reap the benefits of bilingualism and so it makes sense, as a first port of call, that we do so by first learning te reo Maori - after all, it's our language."
Continuing monolingualism brings a danger of New Zealand being left behind and becoming more isolated, he added. "It's time we caught up with the rest of the world."