What year are you in?
I know it’s tempting to try to plan everything out ahead of time, but for graduate study, interests often develop organically over time. If you haven’t yet taken any introductory courses in either area, or if you are just finishing your first semester of them, give yourself some time. Intro classes are designed in part to expose you a bit to different areas of a field. As you learn more about your fields, you’ll learn more about what classes are both necessary to do well and get into graduate programs as well as what classes are fascinating and feed the abiding passion you have to do work in those fields.
In order to get an idea of the first one, you might visit the websites of some top computational linguistics PhD programs and see what their recommended prerequisite coursework is. If you can find a forum where graduate students in that field hang out and chat or lurk you might glean that information that way. You can also talk to your linguistics professors, because they’ll know - especially if there are any computational linguists on faculty.
As far as interests - well, you don’t know what you don’t know, so to speak. Once you take a couple classes you will start to formulate an interest area, and those will guide the upper-level classes that you take. Also, it’s fine to explore a bit in undergrad school. I’m a health psychologist by training and I never took a single class in health psychology in undergrad, although I took classes in related subfields.