Use NUsearch, Northwestern University Library's search tool, to find books, documents, video, sound recordings, and other items across both the Evanston and Chicago campus libraries of Northwestern University.
NOTE: NUsearch can also search across several article databases to retrieve articles and other documents.                                          

multilingual* AND code-switching-> finds both multilingual and code-switching in the book or article records / descriptive content.

multilingual* AND (code-switching OR "language alternation")--> finds multilingual and code-switching, or multilingual and "language alternation" or all 3 terms or concepts in the book or article records / descriptive content. 

Since code-switching and "language alternation" are synonymous or related search words, combining them with OR in the same search may broaden your search and help discover relevant sources that you might have otherwise missed.

The initial search below in NUsearch finds not only books, but journals, individual articles and many other formats for information sources.  You can easily limit down to any format or date of publication, subject, language, etc.