"play a role in the major national security challenges"

If the Middle East is their focus (though our major national security challenges could well be much closer to home to our south, the nearest source of growing instability and migration to the US; or Asia, where the economic focus will continue to shift, with resultant competition at a variety of levels and venues between the US and emerging nations there), Arabic is always a safe bet.

I believe that Iran will re-emerge as the enduring Middle Eastern nation, hopefully as a strong US Ally. If this student is more interested in shaping our future than our past, I would recommend Farsi.