system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How did the Navajo communicate and why couldn't enemies decipher the language in World War II?

What's so special about the language (besides its difficulty, I assume) that makes it so hard to understand?
gpt
It's a bit more complicated than just being a language not spoken outside of the Americas. It's also because it's from a language family that's not spoken outside of a small group in the Americas. This is important because it makes it about 50 thousand (citation needed) times harder to translate it.

Take for example the English language. English comes from the Indo-European family of languages. That means that it has at least some similarities to other languages in this family, including all of the Romance languages and all of the Germanic languages, etc. So even with no understanding of English, if you know one of the many languages in that language family, you at least have a baseline.

Then compare Navajo. Navajo comes from a family called Na-Dene which, until very recently, was believed to exist only in the Americas. Even still it only existed in small parts of the Yukon and the North.

As an aside, we now know that there are tribes in Siberia who speak a similar language but that wasn't known at the time.

So, this being a language not widely spoken, from a language tree that isn't spread outside of our region, with no baseline for other countries to use in their codebreaking, made it a very convenient and efficient language to use.