I think the initial attack was for resources (like a massive amount of relatively clean liquid water). Due to their technical superiority I don't think it normally cost them much to find and/or defeat planets this way. Until us.
This second attack I think is more of an "oh sh*t!" moment where they have lost an entire attack force and their tech is now in the hands of a species likely capable of using it. Lets see if we can wipe them out before they come looking for us, and if we can recoup some natural resources too that would be swell.
I dont think there was any loss of translation. He was shown images of this almost unimaginable large attack force moving from planet to planet and striping them of everything useful. One could easily assume this is an entire civilization moving itself place to place. Or he could have easily seen several such attack groups doing this while realizing it was their entire civilization.
Based on the sheer size of the craft crashing, and the relatively intact nature of it, I wouldn't be surprised if some aliens did get out (and the website linked here says some did escape).
As far as adapting the tech goes, it was the aliens who first adapted their tech to ours. They thought it would be clever to utilize our own satellites since they were there...that created the back door that let us into their source code or what have you. It's not like we immediately knew how to use their stuff either, just how to break it. It takes 20 years for us to have adapted the tech to the point in this new movie.
In the real world we already have lasers and rail guns and plasma tech. Our problem is more of a power issue. If we could utilize just the alien power tech we could create some crazy "sci-fi" weapons. Utilizing any of their other tech to advance these designs could make them seem alien..
This looks like a plausible story line. The first attack was actually a resource collection fleet. Once they went missing, or the survivors sent word they ran into an intelligent species capable of resisting their attack. They send a battle fleet that is many more times powerful.
I just hope we dont defeat them in some cheesy way this time around. Or better, we lose. I would like to see one movie where humanity loses to a superior alien race.
