The Scouts to the Rescue! serial in question is here, in two parts:
The serial of course is aimed at children and isn't really trying to "accomplish Native languages"; it's doing Peter Pan stuff, with buried treasure and Indians and gangsters and so on. In fact, given the context I'd expect that this isn't even an Easter egg from the guy who mixed the audio — I'd think of it more like an Ovaltine decoder ring, a deliberate little puzzle for the kids. (See also Pig Latin.)
You can decode the Indian talk with an online gadget like this one, if you can't find your kid's Yak Bak. The first several instances of "Indian talk" are at:
- Chapter 1 @17:27: "White [strangers?] come! Whites [only?] come!"
- Chapter 2 @28:00: milling about, clearly reversed but unintelligible
- Chapter 2 @28:33: "Tell great chief. Many white strangers leave. Some stay." (The lips are readable in this one: the actor is really saying the English lines, and the video is not reversed. This is immediately followed by a subtitled message on the drum: "Some white strangers go. Many stay.")
- Chapter 2 @29:13: two sections, both definitely reversed but unintelligible, both sound non-English to me
- Chapter 2 @29:21: "Where's [Likoku?] Send the [icing?] to our hideout! Send message! [Please hurry?]"
- Chapter 2 @39:49: "Tell great chief: White strangers come into hills. Fast like wind." (The lips are readable in this one: the actor is really saying the English lines, and the video is not reversed. This is immediately followed by a subtitled message on the drum: "White strangers come into hills fast like wind.") Immediately followed by...
- Chapter 2 @40:02: "Send message. [It's Lloyd Daniels?] Stop white strangers." (The lips are readable in this one: the actor is really saying the English lines, and the video is not reversed.)
- Chapter 3 @46:52: As the Indians mill around, some plausibly "Native language," perhaps; doesn't sound reversed and also doesn't sound like English. "...um-patiha, tiha; el, dal-a-ji..."
- Chapter 3 @48:23: "Tell great chief. Many white strangers stay in our hills." (Lips unreadable. This is immediately followed by a subtitled message on the drum: "Many strangers remain in our hills.")
- Chapter 3 @49:00: [...]
I initially intended to list all of them, but it turns out there were a lot, and I ended up with better things to do. :) Maybe I'll come back and expand this answer later.