Of course this expansion is also designed by Cathala, and the contents of it match the summary presented in a March 2014 BGG News post. In more detail:
Like their fellow tribes from the base game, these artisans are represented by meeples — purple ones in this case — and players will collect them and use them during play to craft precious goods or magic items, with some of these items being worth victory points (VPs) and others unlocking special powers for their owner.
Artisans can't just craft things out of mid-air, though, so you'll need to visit the new tiles included in this expansion to allow them to perform: workshops (where the artisans craft their items) and specialized markets (where players can purchase specific merchandise that they need).
Various other bits are included in the expansion, such as an additional tile that features an impassable chasm, and this tile — as well as the included mountain markers — forces players to adapt to new landscapes when moving meeples on the board. Five Tribes: The Artisans of Naqala also includes two new Djinns.
Six tribes now? Hmm, perhaps Five Tribes should be renamed Six Tribes — but the base game still includes only five tribes, so that wouldn't work. In a press release from Days of Wonder, Cathala says that he knew five wasn't a hard limit for the number of tribes one might find in play: "I knew that sooner or later, a new tribe would appear in Five Tribes. Artisans bring some variety in the Sultanate, yet they do not break the balance of the game – but you should not ignore them as their magic items can be very powerful. The new mountains and chasm also ensure a lot of replayability as moving meeples on the board will not be as easy as before." Anyone want to speculate now on the color and power of tribe #7?