I think, since alien's 12-part message isn't really important for the plot, they simply skipped it but it is sort of implied - or even mentioned at some point, I think? - that countries were eventually exchanging those pieces of info between them and likely pieced it all together. What bothers me is how Renner's character really came to the conclusion that what they got is 1/12 of the whole? Aliens were 'painting' the message to the glass wall, but when he showed it in his computer it was in 3D space with width, height & depth. Then, how would he know how big is the 'box' containing full message and how densely packed the symbols are to calculate that what they have constitutes 1/12th?
Regarding language, I guess your interpretation is correct (at least aligns with mine

), but again I have issues with how they come to this. How do you go from "writing a sentence with 2 hands simultaneously from left and right requires you to know the number and length of words" to conclusion, that it means time is non-linear for them and they know the future? If I wanted to write a sentence using my both hands and even legs simultaneously I'd just need to know the sentence and practice my writing and spacing for a bit... That's it.