In addition to searching Summon by keywords or phrases (such as "Modern Greek"), you can search by Library of Congress Subject Headings such as those below.  Click on Summon, then Options to the right of the searchbox.  Now use the dropdown at the beginning of the searchbox to select Subject Terms.  Type in Subject Headings such as:
     Greek language, modern
     Greek literature, modern
     Children's literature, Greek (Modern)
     Folk literature, Greek (Modern)
     Greek American Literature
     Greece 

You can also limit lists of results by those in specific languages using the Languages dropdown in the left-hand column.