Tagalog would have probably been very useful when i was an Air Department DIVO in Westpac. Could have understood the ABHs' sh!t-talking
Otherwise, already mentioned, not as an aviator.
Already knowing a language well enough to test 2/2 would help you on the lat transfer board if you want to be a FAO. Might even get you some extra $$ if you become a FAO.
Other than that, not really advantages. Knowing other languages doesn't hurt, for sure. But just don't think that knowing one will necessarily make things better for you (other than the $$). We have no shortage of native Mandarin/Cantonese and Russian speakers in the Navy (for better or for worse). As a FAO, French will get you a one-way ticket to AFRICOM, so if that's your thing, go for it. Spanish...? We're not hurting for Spanish speakers.
Arabic...this is an interesting one. We don't have a ton of native speakers, there's a high demand, and it's very difficult to learn. So if you know Arabic your ability would be in demand. But would you want to do multiple tours in the MENA region?