On the ferry to La Gomera, the trip information was in 3 languages, Spanish, english and whistling!
Some resources on the whistling language of La Gomera
Unlike many languages this one appears to have hope of being saved, this article describes its origins and says that it is now taught in the schools on La Gomera.Shepherds whistle while they work and brains process sounds as language
Here is a BBC sound file about the language
Compare the above to a whistled conservation from the Chinantec region of Oaxaca and Veracruz, Mexico. Article and sound files here