Foreign traders travel in caravans of many traders at a time. They are neither aggressive nor afraid of the player character. You can sell furs to them in exchange for iron armour they frequently offer. Foreign traders accept the most valuable furs as offers for their items when trading, such as fox fur,seal fur, bear fur or lynx fur (at v318stable fur clothes don't satisfy them, must be furs). They also take metal items, such as armor or weapons. They are hostile to the player when the player finds them in the Njerpez cultural zone. Killing foreign traders can be extremely lucrative for well-armed and experienced players, but make sure not to underestimate them. Foreign traders usually do not travel alone, with their companions often following from a distance. The companions are able to aggro from far away, even when they are asleep.
Annoyingly, like other wandering NPCs, they can have a tendency of hanging around the players settlement or shelter. This prevents travel on the over world map directly from that location and they have a habit of picking up "unclaimed" items.
As of version 3.15p1, they may be the sole source of masterwork shortbow, longbow, and high quality arrows(possibly bought from the reemi in their bowyer shops). Their other wares can be found at Drik shops, but the above are pretty rare.
Also, as possessors of high quality weapons and armors, they can be considered more dangerous than Njerpez. If you decide to kill one group, make very sure that no survivor escape, or they may return to fight at inopportune times.
At 3.19 traders can be trapped with your trap pits with sharp stakes. Falling to player's trap don't make them hostile to the player, so if one (or two, or three) of them bleed to death because of your traps, you can take the loot, and other traders from the same caravan will keep friendly trade with you. Kind of exploit, maybe.