I think often in dramas they explain some words that you might not know if you're watching only the dramas about nowadays. If anything, you can look it up on google and you'll find the answer pretty soon.
2 historical dramas I really enjoyed were Moon Lovers: Scarlet Heart Ryeo, which was a little bit modernized on the vocabulary part I think, and Mirror of the Witch -- which was my first historical drama and is still my most favorite one.
I am currently watching Rebel: The Thief Who Stole The People, and while it does take me some time to move forward with the episodes, I think it is also a very good historical drama.