In essence, most of the conflicts in New Caledonia have been a clash of cultures. For more than a century, the Kanaks have been obliged to adopt a foreign way of life that styled itself as superior to their own. Yet despite the Kanaks' acceptance of a foreign language, religion, dress, and a monetary economy, indigenous custom (la coutume) continues to exert a surprising hold beneath the surface. The term la coutume has many meanings, and in the case of visitors it sometimes refers to a small gift (usually money), which can be given to show appreciation for some favor. If you're granted permission to camp, allowed to visit a custom area, or invited to stay in a local home, it's not amiss to offer la coutume.
Twenty-eight indigenous languages are still spoken, all of them Austronesian. They can be broadly organized into eight related areas: five on Grande Terre and one on each of the Loyalties. The Kanak languages all developed from a single mother tongue, but are today mutually incomprehensible (thus it's incorrect and denigrating to call them "dialects"). Lifou is the language with the most speakers: about 11,000 on Lifou itself, plus a few thousand in Nouméa. French is the common language understood by most. Very few people in New Caledonia understand English and you'll get a lot more out of your stay if you know a little French.
Most of the people you'll meet in New Caledonia will be friendly and helpful, but there's a small minority who are out to rip you off. If you pay for anything with a CFP 10,000 note, watch carefully what is happening, as the person may try to distract you by asking for small change or something else, then switch your CFP 10,000 note for a similar looking CFP 1,000 bill and claim that's all you gave them. Credit card fraud is also not unknown in New Caledonia, and if you sign a charge slip to guarantee a rental car, for example, it's best to let the charge go through and not offer to pay cash in the end or you could be billed twice. Don't let your credit card out of sight for a moment, no matter how nice the person may seem on the surface. Verify all charges beforehand. It's usually the métros who play these tricks, and you shouldn't go by appearances.