Research the language requirements for different study abroad programs. Take great care in choosing the program you want to apply to. Your language skills and goals will factor into which program you would like to take part in. Some universities may have courses offered in English, though you will most likely be taking classes in Spanish. If you are interested in a semester or year abroad, the university in Spain might require you to study Spanish as well as your law classes, or to take a qualifying exam before enrolling in regular university courses. In addition, your home university may require a certain proficiency level of Spanish for acceptance to a study abroad program in Spain. If you wish to complete your entire law degree at a Spanish university, you will need to complete the application and as well as a Spanish language proficiency test, which may vary from school to school.
Mention your specific goals regarding the study of law and your reasons for wanting to study in Spain when applying to a study abroad program. The fact that you know what field you are pursuing is an indicator that you are a mature student who takes her academic studies seriously. Detail why you want to study law and where your future aspirations lie in regards to this pursuit. Explain why you want to study in Spain and how this will help you reach your goals after graduating from law school. Be as specific as possible. If you have a particular school in mind, research some of the courses you would like to take and the professors you would like to work with and mention these details in your statement of purpose.
Apply to universities on your own. You can take summer courses or take a semester off from your regular university to experience university life in Spain. This is an option if your school doesn't have an adequate education abroad program for your goals. If you do your law study in Spain on your own time, such as during a summer program, you can still receive the credits you need during the year to graduate on time.