In Spanish the suffix -ISTA can be added to the names of areas of law to designate a person who specializes in that area, either as a scholar or as a practicing lawyer.
There is a similar practice in English. For example, a "medievalist" is a scholar who studies the Middle Ages. But that practice doesn't extend to the names of legal scholars, and therefore, there is not a one-word English translation for the following:
civilista - civil law scholar
penalista - criminal law scholar
constitucionalista - constitutional law scholar
mercantilista - commercial law scholar
laboralista - labor law scholar
procesalista - procedural law scholar
comparatista - comparative law scholar
The terms above can also be used to refer to a lawyer who practices in a certain area. Thus, penalista can also be translated a "criminal lawyer" (meaning one who specializes in criminal law, not a lawyer who is a criminal). By the same token, laboralista can mean a "labor lawyer" (one who specializes in labor law). Note that a labor lawyer is not necessarily one who represents labor (employees and labor unions), but could in fact be a lawyer who represents employers in disputes with their employees and labor unions. The idea is that the person practices in the field of labor law (also called "labor and employment law" in English).