The whistled language of La Gomera Island in the Canaries, the Silbo Gomero, replicates the islanders' habitual language (Castilian Spanish) with whistling.

UNESCO: Culture

Which brings us back to de Boinod's title: tingo is an invaluable word from the Pascuense language of Easter Island meaning "to borrow objects from a friend's house, one by one, until there's nothing left".

BBC: NEWS | UK | Magazine | Tingo, nakkele and other wonders

The island's then chief minister, Tony Brown, also wrote to UNESCO claiming the language was "still flourishing on the island".

BBC: New app launched to 'boost' Manx language revival

That's what the Hawaii university researchers say happened -- even if few realized that a distinctive sign language existed for decades on the island until now.

CNN: Researchers document distinctive Hawaii Sign Language

Statehood or no, there are plans for English-language science and mathematics classes in the island's schools.

ECONOMIST: Empire in the Americas

Donna Long, a lifelong resident of the island, has four sons who all attend the Manx-language school.

BBC: Manx: Bringing a language back from the dead

As for Jeju, it is a critically endangered language spoken by no more than 10, 000 people on Jeju Island in the Republic of Korea.

UNESCO: MEDIA SERVICES

Sardinian is not widely taught in schools on the Italian island and has a largely oral tradition, which means there is currently no standardised form of the language.

BBC: Bilingual children 'better at problem-solving skills'