Wrong Language

At the end, Duncan is translating Hawkeye's English into French for the chief. Magua also speaks French and replies as such for Duncan's (and Hawkeye's) benefit. Seems like Hawkeye, man of the woods that he is, should know some Huron though.

WRONG!

At the beginning Major Duncan doesn't understant Maqua because he's speaking Huron, true. But later in the film at the village everyone is talking french. You can even hear Hawkeye tell Duncan to translate what he said to the Huron elder in French.

I have not seen the whole movie the entire way through for some time, so I'm not certain what language Magua is speaking when he is their guide. Let us assume, for arguments sake, Magua is speaking the language of his tribe. But, during the scene in the village, which I do remember very clearly, Duncan, Magua, and the tribal elder are speaking French, or something that sounds very close to French. That would explain Duncan's inability to understand Magua earlier.

no...

The reason that Duncan can translate is {if you listened} Nathanial/Hawkeye asked if the Huron could speak French {which they could, since they were French allies} and had Duncan translate what he said into French, since that was the only common language they would have had. If you know even a little bit of French, you can tell he is speaking french by the way he sounds, and Magua says "Je curse vous" which is french. When Magua was responding to Duncan he was speaking in his own Huron tongue.

Multiple Languages

In the last scene at the Huron village, Duncan is translating Hawkeye's English into French for the Huron chief. Magua also can speak French, which he does when speaking to the chief for Duncan's benefit. Duncan translates their French back to English for Hawkeye, who surprisingly appears able to speak only English (and Mohican). Seems like Hawkeye would learn at least some of the language of his enemies. Odd that only the villainous Magua can speak three languages.

He's speaking French

In the indian village, I'm pretty sure that the resaon why Major Heyward is acting as a translator is because every thing is spoken in French. It is common for this to happen in military history. For example: when Wellington and Blucher met after Waterloo, they had to discuss things using a common language: French.

Nothing confusing here

On the march Magua responds in his native language, later in the village they both speak french which the Hurons being the allies of the french did understand as well as Duncan.

Um, French, duh.

In the beginning of the movie, Magua speaks Huron. Duncan doesn't know Huron. At the end, Magua and the Chief speak French. Duncan speaks french. I know neither language, but it doesn't take a rocket scientist to figure this one out...