@roger,
No, not just local interest at all. I first remember reading about this in the Readers Digest, about twenty or more years ago, and found the whole thing fascinating. It was reckoned that they were much much more effective than the German code machines, and it was instant.
I've just looked up the film. Wndtalkers was released in 2002, and starred Nicolas Cage, but despite that, received a reasonable rating.
Have they managed to keep the language alive in any way, shape or form?