I was working with the Airport police yesterday with an asylum seeker from Afghanistan. I spoke Farsi, she spoke Dari. I had heard Dari before and knew this sort of Farsi-Dari communication was possible and as no Dari interpreter was available, I was called in. I knew it would be hard but I have to admit, I did't expect I'd have so much trouble understanding her.
After about 20 minutes the lady said in Dari, "let me try to speak in English, because Dari seems to be hard for you to understand". I automatically thought, well.. my Farsi is poorer than I thought.
The thing is, if you speak Farsi really well, in theory you should be able to understand Dari pretty well too, so I thought it was clear the problem was my Farsi and not the fact that I didn't understand Dari too well.
I continued speaking in Farsi and she spoke in English. After about an hour she asked: Where are you from? I said "Here." and pointed to the ground. To my surprise, she asked: "You are not from Iran?"