2/2 is limited working proficiency, far from advanced proficiency.
2+/2+ is the minimum requirement for CTIs to graduate DLI and "A" school, and 2/2 is the bottom-of-the-barrel requirement for them to not be re-rated out of the CTI rating.
The jump from 2+ and below to 3 and above is also significant, as it is the jump between the lower level DLPT and the higher level DLPT under the new electronic test.
Most of the common languages were marked "Prevalent in Force" and scrubbed off the payment list a while ago (Chinese, Russian, and the Standard Arabic being among them). There's some really obscure ones that will still be paid. This wasn't always the case in the past and won't always be the case in the future, but currently we've trained enough professional linguists through DLI for most languages that you can think of and we don't need to incentivize amateurs.
Assuming the language in question is PIF, in most cases the Navy pays exclusively by billet or by training (attended DLI or other formal DOD language training--which is not just classes in college).
This means generally officers will not be eligible for FLPB unless they have attended DLI (mostly FAOs, NSW, EOD) or they are in a billet with a coded language requirement (mostly FAOs, others in something like an attaché billet or some special thing). For example, officers who are selected for the Olmsted Program will be sent to DLI, will meet that eligibility criteria, and will be paid as long as they take the DLPT every year and get the scores.
It is unusual for CW officers to hold language proficiency (here meaning enough proficiency to score a 2 and not just scrape out a 0+ or 1) nor is there any program for them to acquire it. The ones that have proficiency and receive FLPB are mostly prior CTIs that remain eligible due to their DLI training and have continued to take the DLPT annually. I'm sure there's a few out there that did stints with SOF or something and also foundation themselves at DLI or similar training, but that issues was nothing usual.h
B
FAOs do six months of in-country training. I think ao t key difference between the Navy and otherre WA services is that Navy FAOs are assigned but region18 and may not necessarily be assigned to a D- country based solely on their language proficiency (i.e. Far East FAO that learned Chinese at DLI can still be assigned to Japan or Korea).