Encyclopedias are for answering questions that have known, generally agreed upon answers--the fact-based "who," "what," "when," and "where" questions. For "why" and (non-procedural) "how" questions, you usually need to do research in books and journals.
To search specifically for books in Boatwright, use the Library Catalog. When dealing with a topic that can be used in many fields it is best to add a second word that describes your area of interest. Remember that books are generally on broad topics and that you are not searching the full text, only the titles, subject headings, and--if you're lucky--the table of contents. You can also use Onesearch and limit your results to items in the library catalog. Book reviews can also be extremely helpful in identifying the most useful books. For narrower topics, search for journal articles in Find Articles or in a journal database such as Communication and Mass Media Complete, or one of the others listed under the "Articles" tab.
Below are some subject headings you may find useful:
Language and Culture--United States
English Language--United States
Communication and culture--United States.
English Language--Social Aspects--United States
English Language--Dialects--United States