I love learning about different dialects and I own all sorts of regional and time-period slang dictionaries. I often browse through relevant ones while writing a story. I also read a lot of diaries and oral histories.
Dictionaries are like watches the worst is better than none and the best cannot be expected to go quite true.
The human imagination... has great difficulty in living strictly within the confines of a materialist practice or philosophy. It dreams like a dog in its basket of hares in the open.