A Transformer's alternate mode (common name for vehicle mode) has to fit within certain boundaries, and they use holograms and other minor tricks to make this alternate mode look like something similar to the world they're on.
As such, a Transformer with a car altmode may be able to choose what kind of car within a range of cars he transforms into, but he ...
Why did Optimus Prime tell Sam Witwicky to push the cube into Primes chest instead of just attacking Megatron with it?
I seem to remember it was somewhere stated that Megatron was (a lot?) stronger/more powerful than Optimus. So Optimus probably deemed it too risky to get the cube anywhere near Megatron where he might actually get hold of it. Optimus ...
Frenzy is a sort of special case.
Frenzy is exceptionally hard to kill, due to the fact that he possesses a de-centralized, modular nervous system. In essence it means that even if he suffers critical injuries—such as getting his head severed, which seems to be a not-infrequent problem for him—he can continue to function.
Megatron had been ...
According to the film's official novelisation (by Alan Dean Foster) it wasn't a jet fighter, it was merely jet-fighter shaped, perfect for escaping at high speed from the hangar.
As to how Megatron had managed to create one, given the unique design of the "alien aircraft", it's most likely that Megatron scanned it before setting off for Earth:
First, we should address this claim:
almost all Decepticons have military alt-modes
Let's go down the list of Decepticon alt-modes from the 2007 movie:
Megatron: Cybertronian Jet. No Earth-based alt-mode. Not military.
Starscream: F-22. Military.
Blackout: MH-53J Pave Low III helicopter. Military
Scorponok: Scorpion. Not military
Frenzy: Boombox, ...
This is simple supposition, but I would imagine that the language could be communicated fairly easily from Starscream(or another Decepticon) to Megatron. These are advanced machines, it isn't like he has to put his spectacles on and sit down with a copy of English for Dummies, he should be able to just download the language files from another.
It is a detail that most likely got overlooked by the production team. But also may be because this led to the rather funny running gag where BumbleBee cannot speak, and talks only through radio snippets. Sadly no in-universe explanation for this.
Are we supposed to just forget this or was there an explanation that I missed?
While this sounds a little facetious, I think that you are supposed to forget. Continuity in the Transformers Movie franchise has not been one of its strong points.
In any long running series, you are going to struggle with continuity. Even in cases where an author has sole ...