On many of the pages that you'll see in Accelerated Reader and on many of the reports, the quiz language is identified. Often the language is simply indicated by an "EN" or an "SP" near the quiz number. Any time you see this, EN means the quiz is in English, and SP means the quiz is in Spanish.
If you want to hide Spanish quizzes, an administrator can use the Locale Content Sets preference to change the availability of those quizzes on your site.
Students are allowed to take both the English and Spanish quizzes for the same title if both are available.