Kevin,

I agree with a lot that's been said here, so I'll just reinforce some points.

As someone who has undergone formal and informal language training for seven different languages (including Russian which I barely get a chance to speak), start with selecting a language you will be motivated to learn and one you can use often.

Learning a language is a hard slog, so spend your time doing something you will get a lot out of.

As an MI Officer, if you need to retrain in another language, no big deal. Once you've had a positive experience learning a language, you can take on another. It's time-consuming, sure, but it will be faster the second time around.

Btw, RE cultural proficiency, you'll learn it along the way, not in a classroom.

All the best!