You're doing the right thing in pursuing a language. Some thought on how to pick one;

1) Pick a language spoken in places you'd like to go. If you don't like cold weather, don't study Finnish (Finland is a great place, but only has about three months a year that aren't bitter cold). My next project is studying Bahasa (Indonesian). There are terrorists there, there is snorkeling to die for, and they grow coffee and chocolate; my kind of place. This leads into...

2) Pick a language that is needed. Latin is a great language for a number of reasons, but only spoken in Vatican City, not of great utility to the DoD.

Which language? Mandarin, Korean, Urdu/Hindi, Russian, Portuguese, Spanish, French, Afrikaans, and Arabic are all fairly obvious and needed, but Chinese dialects, Central Asian languages, Pacific Islander languages and less common Pakistani and Indian languages are needed. A slightly obscure language would really make you stand out from the crowd. (In most somewhat metropolitan areas) you can find a club to help you.

Check out relations between languages before settling on one. Dari and Farsi (by reputation), Serb and Slovene (by personal experience), are closer pairs than Spanish and Portuguese. On the other hand Mandarin and Cantonese are fairly far apart despite being both 'Chinese'.

I understand the reservations expressed by others about the lower density languages, but it is good to hear conflicting positions. I'd skip on Spanish as the Army has many people who grew up speaking New World Spanish, and the need for additional speakers is not great. I'm not sure I agree with the earlier comment about left over Cold War Russian linguists; they're retiring rapidly, and most are at a point in their lived where field time is less attractive (or practical) than it used to be.

I'm not sure I agree with 120mm about "Your goal for being an officer should be to lead soldiers, not do a job or speak a language." The Army is a big place and needs a lot of MI officers who aren't in traditional troop-leading positions. If you're dead set on being an MI officer, go forth an conquer, but know that it might be a challenge to get to where you wish to go. I can completely understand someone whose Army career aspiration is to be a '2' or 'asst. 2' for 20 years. It's hard to do, but I understand the desire, and if competent, that officer is no less valuable than one that commands a battalion as the apex of his or her career.

@120mm - this will circle back to the old dispute about "all officers are leaders first, last, and always" vs. "balance of staff and leadership officers" if we're not careful. A whole seperate rant...