What was a key characteristic of the Navajo language that made it suitable for coding?

The Navajo language's complexity and uniqueness were pivotal in making it suitable for coding during World War II. The intricate structure and vocabulary of Navajo made it difficult for non-Navajo speakers to decipher the coded messages. The language includes a variety of sounds and phrasing that do not have direct equivalents in other languages, contributing to effective communication that was secure from enemies. Additionally, its oral tradition and rich cultural context provided a wealth of terms and phrases that could be creatively adapted for military use. In contrast, other options like being widely spoken or having simple grammar do not provide the same level of security or difficulty in interpretation, which are critical factors for effective coding languages in wartime scenarios.