Nearly all dervishes belong to nomadic cultures. These nomads are not simple wanderers with no roots to call their own - they have their ancient traditions, and their societies simply do not consider permanent settlements an important part of their nature. They are gypsies, keeping their own traditions and forging their own familial and societal bonds while they move throughout the world. Often, these tribes adopt the attitudes and even some of the laws of the lands they live in - for the sake of expedience, if nothing else. The dervish treats fighting styles the same way. A dervish learns the dance of war as she grows up among her family and her tribe. She watches others as she travels, however, and brings new steps to the dance as she goes.
This strongly suggests that the Dervish class in itself is a discipline borne from multi-cultural roots, thus making a strong case that a Dervish would naturally have at least a passing knowledge of different lands and cultures. Ergo, a class skill
What are your thoughts, guys?