Use the advanced search to look for Webster's Dictionary in the title field and select the time period that interests you.
You can do the same thing using the subject field with Americanisms (aka slang) and Quotations, to get a flavor of the speech of the day.
The word to search for a dialect is, conveniently, dialects (yes, plural) and the name of the language, e.g., Irish. Some of the material you find may be very oriented towards linguists. If you have too many results, try adding in dictionaries (yes, plural). Again, make sure that you're doing a subject search.