OP: you have gotten good advice. Still, I had to weigh in with my experience. I took four years of German. Not much help unless you get stationed there (Marines don't!). A good 50% of my platoon was Hispanic and in some ways, I wish I would have had a better understanding of the culture and language.
Interesting side note: I don't know if it was universal, but in my Battalion there was a standing requirement to speak English when you were working, in uniform, or in the field. The exception was private, off-duty conversation. The guidance was that they didn't want groups divided by language or disrespecting Officers, NCO's or other Marines by hiding behind an alternate language.