You are correct in that language selection is based on your DLAB score for those that do not have a DLPT rating in another language. For those that do have a rating its a whole other ball of wax.
There have been guys who test out of a language (DLPT) and then get selected for another language altogether while some test out and only have to attend blocks 1 & 2 of language instruction (these guys are AI's) in the language they tested out of.
The fact of the matter is it comes down to the needs of the Regiment first. And until you get to SFAS you will not know what language you will get, unless of course you are a NG Candidate.
HTH,
Crip