Yap practises a rigid caste system creating an additional element of control over would be trouble makers. So, as long as you are culturally sensitive and respectful, you will be able to experience an entire cultural immersion. Do not wear shorts in public, except at beaches or swimming areas - showing the thighs is considered vulgar and immodest.
talk
Yapese, Ulithian, Woleaian and Satawalese are the island's official languages all of which are indigenous, but English is also spoken by many of the locals and travelers will have no problem getting by knowing little if any of the indigenous languages. Many of the elderly Yapese people are fluent in the Japanese language as well.