Airborne linguist and ground cryptologist linguist are two very different experiences. I would try and decide what you prioritize. Airborne's op tempo is much higher usually and you can get pigeonholed but you get to fly and usually do cool missions. Flight pay and being a flyer is pretty cool.
With being a ground linguist you have some more stability and I would argue working in the Agency can give you more opportunities to branch out. Being a linguist is just like any other job in the Air Force though it's what you make of it. I wouldn't recommend airborne over ground everyone has different goals and preferences in life. If you want to travel as much as possible though airborne is def the right choice. Lmk if you have any other questions.
Also if you are worried about the DLAB just buy this book and you should be fine.
Worth a look, I used it. Very helpful, does take some effort but you can get itt down in 2 weeks.
Everyone is going to say you can't study for it. You absolutely can, but only so far.
There are two books I recommend linked below. Read them and do the tests. One claims to have the rules for the test but it's outdated, don't trust it.
In addition, study basic English grammar. Understand the basic parts of speech, understand that not all languages have the same syntax as English. Maybe study the grammar for a Semitic or Asian language to get an idea of this.
If you're intelligent you should do fine.
https://www.amazon.com/Complete-DLAB-Study-Guide-Practice-ebook/dp/B00KMHFXCQ
https://www.amazon.com/Official-DLAB-Training-Manual-Practice-ebook/dp/B00HUC6RT4
u/lamont196 is right on.
DLAB is a made up test to assess your ability to learn a new language. DLPT or OPI is to test out of an actual language - meaning you've rated proficient in Spanish or Russian or whatever language.
DLAB is a crazy test and was pretty challenging for me. I used these two books to prepare for the test. It helps familiarize yourself with the test and gave me confidence going in. The practice tests were very helpful. I'm not great at languages but was able to qualify for Cat 4 languages. Talk to your recruiter and see if it's possible to get the DLAB or DLPT/OPI done before enlisting - it's just one thing you won't have to worry about down the line. Not sure if that's possible for the DLPT or OPI but worth checking.