The best way to identify an international or multicultural book is to generate a set of search terms that may include:
Country of origin (e.g., United Kingdom, Aftrica, etc.)
Description of race (e.g., African American, Asian, etc.)
A specific historical event (e.g., World War II)
Use of the word international
Use of the word multicultural
The quickest way for you to identify young adult authors is to do a Google search. If you don't know the name of an author, try searching "young adult author AND (country)."
Many of the various links in this Libguide can help you identify authors as well.