Hmm, I've developed to varying degrees a variety of barbarian cultures, but the more technologically-backwards of them are pretty well removed from the Renaissance-era center of the setting. The two prominent sources, a seafaring, plundering, horse-archering Central Asian culture and a mountaineering, more landlubbering, variously civilized Scandinavianish/ Pictish culture, both have weapons tech, steel, siege, on a full mid-medieval level, chain armor, good-to-very-good weapons. Arcane magic is more primitive, but wizards can be found and they work just like wizards elsewhere... I use binders to represent a more primitive form of magic, and the Central Asian area is home to what binders there remain in the world.
Further out there are the remains of fallen cultures. One group knows bronze and the other's solidly stone-age. The first has a few sorcerors pop up now and again, and the second does not know arcane magic at all.
I just use some of the UA totem variants to shade the differences between barbarians mechanically.
As for places where they may be "barbarians" but they aren't really barbarians, scout and ranger work pretty well for their heroic warrior-types, I don't see a need to screw the barbarian class into the slot. Ranger's solid for the legendary Native American warrior/hunter archetype, for example... I don't even know that you'd have to change anything.