Chechen refusal to speak Chechen

I think it had to do with the film's angle on integrity. All five main characters do their best for not only them, but for others. I think by the time Ahmed is question by the Russians, he realizes that he's formed more of a bond with the men in the house and realizes the pointlessness of this fight for land.

It could also be, he didn't feel as if he needed to prove himself to them or because they were the men that let Margus down.

Yea, was wondering the same. My guess is Ahmed was a mercenary from Dagestan or Iran.

They are not chechen troops, they are russians and russians are not welcome in this region. Russian KGB was paying to all sides in this war and russian militaries always make sure that diferent etnic groups of this area kill each other. Often russians kill people themself and after blame on one etnic group agains another, provokating bloody conflicts and even wars.