The terminology "Bachelor of Arts in Spanish" is not really correct. The right way to say it is "Bachelor of Arts with a major in Spanish". That is what they want you to have. However, by saying "or its equivalent" they are letting you know that they are willing to make exceptions to that rule. For example, maybe you lived for two years in Spain. Truth is they probably don't actually care what courses you have had. Their only real concern is that you be prepared to handle the work.