Thank you for taking the time for such a detailed response - it certainly gives me a better idea of what you faced in the field. If you don't mind me asking, what motivated you to spend your own money and time on a private language course? Not many seem to have taken that kind of initiative, but it seems to have been worthwhile. Just guessing, but it seems like you have some talent and interest for languages.
I originally started learning when I was interested in screening for MARSOC a while prior to that. I started out with the Rosetta Stone series, which (as @pardus mentioned) we used to get for free. It's usefulness was limited, to put it mildly. The best thing it did was to get me to "listen" to farsi and how words are formed and sentences constructed. Sort of. I don't think I encountered a sentence longer than about 5 words in the course, but at the very least it helped me identify where the verb was usually placed, how the subject was indicated, and a few other things. Once I found out about the afghan trainer deployment, I jumped headlong into language training.
And yes, I do have a knack for languages; technically I know 5 (English, German, Japanese, Farsi and Dari), but I only speak and read English and the last two with anything resembling comprehension. I can still read Japanese, for some reason...
Also, do you know of anyone that tried to learn Pashto? Dari is difficult enough, but Pashto has much more complicated grammar.
I know exactly one guy that tried....he didn't last very long. Pashto is stupidly hard and it's a very niche language. So taking the time to learn it is really a fool's errand.