I sincerely doubt speaking another language would significantly help your chances at selection for an aviation billet.
AppleCello, the only professional opportunity to attend language training for a Junior Officer, in aviation, would be if you went to a Personnel Exchange Program billet (what I'm doing now). If the host country speaks another language, and you don't speak it, you will be sent to the Defense Language Institute.
ljm9304, I DO receive extra pay, but only because I'm required to speak another language in order to fly with my squadron.
Do a search for DLI, Defense Language Institute, and Language Pay. Go PSU!