That actually was a problem, at least for the USAF, in the 90s when we opened up language pay to everyone. Native Spanish and Tagalog speakers were bankrupting us. Luckily we had some sane minds at work and the program was amended to specify that you had to be in linguist billet to receive the pay.
BTW, native speakers don't necessarily make the best linguists depending on the job.....
"Luckily we had some sane minds at work and the program was amended to specify that you had to be in linguist billet to receive the pay."
Let me amend this statement to say that if you were claiming Spanish or Tagalog for foreign language pay you had to be in a language billet.