since it was a fantasy movie, with a non-existant island peopled by non-existant natives, I suspect the language was made up.
But, on further review, perhaps not.
This sounds like the crowd to ask: Where did the bucktoothed thick glasses-wearing caricature come from? My fluent-and-literate Japanese/American student doesn’t know either.
Not really addressing the OP but might be of interest to some people on this thread, the American propaganda film, My Japan from WWII.
Well, I don’t know about the teeth, but similar glasses seemed to have been worn by a number of Japanese politicians and officers in the period, just from the photos I’ve seen—maybe they Were The Style At The Time, or were the Japanese military’s equivalent of BCGs or something.
I always like to contrast these portrayals with some other posters from the war years. I think all that first poster lacks is a fife and a tricorner hat, somewhere. 
I don’t know about the teeth, but Japanese leader Hideki Tojo wore glasses. Here’s a wartime poster of him with glasses and a toothy grin.
