Speaking the language
Will Duolingo actually teach me how to speak it, not just read and write the language I'm learning?
Nope. I watched a YouTube video on Navajo where they said that the pronunciation is so tricky that in regular classes, they spend the entire first course level on pronunciation.
Plus the grammar is not that easy either. It is no coincidence that Navajo was used in WW II as code that proved to be indecipherable for the enemies. DL’s course offers just a glimpse into the language.