<p>English, French, Arabic, Russian, Chinese, Spanish are the six official languages of the UN. In addition, the two working languages are French and English, with all secretaries expected to be fluent in both. (The French care very very much about their language - check out Nadeau’s The Story of French.)
So essentially the more you can develop your language skills, the better - AP Spanish + AP French would definitely be a way to stand out (to speed your progress up, you can do Concordia Language Villages for French or another language, or Middlebury’s summer intensive program, or other summer intensive programs, I think Penn State has one for a few languages and after completion you could start in French 3 or 4 after the summer.)
Beside AP World and AP European history, you can try and see if a local community college offers specific history or “area studies” classes in the summer.
In addition, join Model UN and look for colleges that are competitive in Model UN.
Occidental has a (competitive) internship program at the UN, too, so look at their admission requirements.</p>