(Obviously there is the "write a big info dump explaining everything" option, but I think it's also obvious that's rarely a good option. ;) )
Take LOKI'S BOY. An important part of the plot revolves around the fact that winter isn't ending when it's supposed to. Though at first the main character thinks it's just an especially bad winter and it'll end any day.
Trouble is, in the Norse world there were only two seasons: winter and summer. So when I say something like, "Two weeks into summer, it was still snowing," I mean winter's lasted two weeks longer than people would expect. But a reader used to that whole four seasons thing is probably going to think, Yikes, they didn't even get spring? How can they not be freaking out?
I have tried to work in some dialogue that makes it sort of clear that summer directly follows winter, but it's pretty hard to make that natural. Which makes me wonder if I should just "translate" those two Norse seasons into our current four seasons, and call it spring, so readers will know what the heck I'm talking about. But I hate doing that when I know it's not true to the world.
Thoughts? Those of you who write in other times and cultures--how do you balance accuracy and understanding?