There are thousands of books on archive.org full of regional speech.
Look into the many non-fiction volumes for true stories, letters to the editor. Newspaper articles, court transcripts, regional digests, religious sermons, essays on an endless variety of subjects and political debates.
Archive.org is a one-stop shop for everything historical.
Castles, wooden tenements, feudal arrangements and everything architectural.
Furniture and transportation, every aspect of daily life and recreation.
War and weapons, culture, high and low.
Commerce, medicine and veterinary medicine.
Rural and urban life and life at sea.
Occupations and service industries, hunting, trapping and cook books all for free download.
Hawking, keeping a kennel, fox hunting and its culture, which means manners, vocabulary and dress.
Sciences as they understood them back then, printing, binding and language.
The histories of inks, paints and dyes, farm life and animal husbandry.
Textiles, trades, and merchant guilds, deserts, lakes and jungles.
Insects, serpents, lizards and spiders, forestry, poaching, smuggling and gardening.
Predators, prey and botanical nomenclature.
Minute details of the Spanish Inquisition, insider information of the clergy and the private diaries of monks.
Etc., etc...