If you want to find all the books (any subject, any author) in a given language, follow these steps:
(1) Click "Command Search" in CUNY+
(2) Type WLN= and then the three-letter code for the language you want (this page has a list of all the codes)
(3) Run the search. Your results will now include both books in that langauge as well as those translated.
(4) You will now need to filter your search results. Click "Filter."
(5) In the filter page, click "Text in a Field" from the Filter Options.
(6) On the filter page that opens next, select "Language (008)" from the pull down list labeled "Filter."
(7) In the Type Text box, type in the three-letter language code again. Click the "Go" button.
You should now have filtered your results so that most if not all of the translated works have been eliminated from your search results.
For earlier posts on this blog about language and other command searching, see this post and this post.