Books: Basic information about searching for books
To limit your search to Spanish language, use the Advanced Search option and click the Language box. Add Spanish, and then fill in the rest of your search details (keywords, for example, or other limits).
Once you are looking at the search results page, you can also use the left column to limit by language.
Note that this language limit includes books with even just a little Spanish content, even if the entire book is not written in Spanish.
Hint for Esearch: because some Spanish and English words have the same roots, you can search for both by using the catalog's truncation symbol, which is "*" For example, searching for democra* will find all the words with that root, such as democrat, democratic, democracy and also democracia. Searching for biling* will find bilingual, bilingualism, bilingüe, etc. If you want only the Spanish term, then spell it out completely (diacritics don't matter: you'll get the same result for poesía and poesia).