Moorea has almost no violent crime. Petty theft can be an issue. Check your valuables at the desk or keep them on you. At least keep them stashed out of sight. Odd things may be taken, like the beat up old sneakers you left outside to dry the night before you are leaving, forcing you to hitch a ride to the bus stop because you have no other footwear to make the mile walk up the road and the pavement is a million degrees and there's broken glass in the margin, and then buy $20 USD flip flops to wear on the plane.
Perhaps due to its lack of reliable public transportation and its outrageously expensive taxi fares, Moorea has a serious drunk-driving problem with both tourists and locals equally guilty. Take particular care when walking or cycling the island's only paved road after dark; it gets pitch-black and can be quite dangerous away from the main villages where you'll also be more tempted to walk or cycle in the middle of the road due to the amount of broken glass on the shoulders.
talk
Everybody speaks Tahitian and French. Anybody working in tourist services will speak enough English to get by, although it's not well spoken by the general public.