The experience in Iraq taught that U.S. Army that one very valuable piece of "equipment" was troops in combat and intelligence units that could speak the local language. That was tough to obtain in Iraq, because Arabic is a tough language for Americans to learn. The pronunciation is a killer and the vocabulary and grammar are quite different from English (and all Indo-European languages). Its different in Afghanistan, where the two most common languages (Dari, a close relative of Iranian, and Pushto, a more distant cousin of Iranian) are distant cousins of English. Grammar is more familiar, but pronunciation and vocabulary is sometimes different (like German, the verb often ends up at the end of a sentence). But troops who have served in Iraq note how much easier it is to learn the Afghan languages, and they do. The army now provides courses that teach troops various degrees of "battlefield Dari" (or Pushto). Dari is more of a common language throughout Afghanistan, but Pushto is the local tongue where the Taliban are strongest.
The army has developed Dari and Pushto training courses that enable troops, after a few weeks, or four months, of training, to master either basic battlefield phrases, to (with the longer course) carry on simple conversations. The more time the troops spend out among Afghans, the more bi-lingual they become.
Many troops, after a four month course, and a year in Afghanistan, are pretty adept (although not fluent) in Dari. This makes a big difference. While using Afghans as translators, or even Afghan-American contractors, is useful, but it makes a big difference if the troops can do the talking on the spot. There are never enough translators to go around, and time is often critical in combat situations.