Why were Nadia and Manh fighting when they first meet? The real bad guys on the ship are pretty obviously not-human-looking.
Everyone on board is suffering from Pandorum to a certain degree, thus everyone is more or less crazy. That is why Nadia attacks him on sight, she's a little crazy, though she calms down afterwards.
Hunting is conducive to sticking together in groups. Scavenging is best done alone if your only defensive strategy is "run and hide." Unless you happened to be one of the hunting albinos, it was every man for himself; as we saw in the film, trusting another non-albino could potentially get you eaten.
Because Nadia was mugging Bower and Mahn had stepped in to help him. Weren't you paying attention?
Did they ever mention why Bower felt familiar with the corridor when he met one surviving crew member who was trapped and why Manh couldn't speak English?
I gathered that he felt the corridor was familiar because, in a huge ship like that, the corridor layout is probably the same on adjacent levels, and he once again encountered a body-hanging-from-the-rafters trap, though it turns out to be a living crew survivor, rather than a rotting, disemboweled corpse, like the first time.
Manh was probably recruited from a country that doesn't speak English. The ship was an international effort so they probably recruited from all over the world.
Mahn probably just didn't remember.
Mahn spoke Vietnamese, and presumable he can't speak or doesn't remember English.
How did Nadia survive for months eating bugs?
There was food seen around her hiding spot where she attacked Bower. It was a 123-year trip so there obviously must have been a massive food supply. Plus Nadia had access to the DNA of every animal from Earth in that room.
Also, you can totally survive by eating bugs, and even keep quite healthy as long as you have large enough supply of the right kinds of bugs.
There is also the algae shown on the ship which is edible. Leland was using it.
Why did highly educated people in a crisis situation lose language and become raving maniacs instead of just maintaining their civilization as most have done over the last few thousand years?
Starvation is a great way to fall into cannibalism. They were locked in the lower levels by the guy with delusions of godhood, and left to fend for themselves. And don't forget EVERYONE on board the ship is suffering from Pandorum, everyone, making them paranoid and suffering from hallucinations, including the people who were locked in the hold and eventually became the ancestors of the albinos.
Gallo does not believe he is god. Nowhere in the film does it state or imply that he believed this, at all, but rather the opposite, as he says "God is dead". Its stated that he believes that he was a king. The passengers didn't do it out of starvation as they were in the cargo hold where there should be food that lasted for their children's children's. There's also the open hyper pods with feeding tubes that can support people for centuries. The passengers went insane and Gallo manipulated them into fighting and eating each other which he tried to do with Bower at the end of the film. It's never stated that they were locked in there, just exiled which does not necessarily mean forced.
Delusions of godhood don't need to be literal. Gallo thinks of the Biblical, Abrahamic god as being dead. However, he has placed himself as the ultimate power and authority who defines the new morality, or lack thereof. Everyone on the ship is his to play with, with their lives having no value to him. The man not declaring "I am God Almighty!" doesn't change the fact that he has a god complex.
He does not have a god complex either. He just wanted to create a new world of albino cannibals which he views as "beautiful" and "perfect", remember? He's a social darwinist, as in he believes that moralistic altruism is weakness while egoism(life eat life) is progress.