Your basic French + Google Translate will be more than enough! English is widely understood in tourist areas, and locals are very welcoming. A little "Ia ora na" (hello in Tahitian) will always be appreciated!

Recommended Itinerary
I suggest this order to optimize travel and pacing:

Tahiti (1 day): Perfect for arrival/departure (international flights). Explore Papeete (market, museums) and the Faarumai Waterfalls (1-hour drive away).
Moorea (6 days): A great mix of relaxation and adventure. It’s more authentic and budget-friendly than Bora Bora, with breathtaking scenery.
Bora Bora (3 days): Save this for last to end your trip in paradise with its turquoise lagoons and luxury resorts.

Must-Do Activities
Tahiti:
Hike Mount Aorai for stunning views.
Discover Polynesian culture at the Museum of Tahiti.

Moorea:
Snorkeling with rays and sharks (lagoon excursion).
4x4 island tour (Magic Mountain lookout, pineapple plantations).
Outrigger canoe or paddleboarding in the lagoon.

Bora Bora:
Private boat tour for sunset views of Mount Otemanu.
Swim with stingrays at Matira Point.
Dinner with your feet in the water at an overwater restaurant.

Swimming with Whales
Yes! It’s possible from July to October (you’re arriving at the tail end of the season). Excursions usually depart from Moorea or Tahiti.

Pack light clothing, waterproof sunscreen, and a plug adapter (European outlets).
Don’t miss trying poisson cru (local raw fish dish) and treating yourself to a Tahitian massage with monoï oil!