Silbo Gomero: ‘Special and Beautiful’ Whistled Language
nytimes.com
nytimes.com
A little experimentation and I found I can whistle quite a few English words, so it's probably a matter of acclimation to vocabulary limits and practice among enough individuals that things become standardized. Using things unique to whistling could augment vocabulary or add nuance, but I don't see any reason straight US English (or other languages) couldn't be used.
I could be way off base, but this is a pretty cool language format.
I plan on trying it with friends and family next time we go fishing/camping/hiking. A little bit of practice and repetition should be all it takes.
If you visit the Canary Islands I highly recommend to check it out.