The jobs available to a modern languages major are quite limited. You would either end up working as a translator / interpreter, teacher, or something completely unrelated. That's not to say studying languages is worthless, though -- quite the opposite really. I recommend that you major in something that will give you broader career prospectives while doing a minor (or perhaps a double major) in a modern language.
One thing you might want to consider would be taking a semester or a full year off to work, travel, and gain life experience so you can figure out exactly what you want to study. In fact, I really recommend that if your situation allows it. Just remember that you'll have to go back to school eventually .
As static said, a second language, even a few years studying one without a cultural immersion, can be extremely useful and open up a lot of doors when coupled with another degree. Being somewhat multilingual is definitely something that companies who hire will be looking for. Keep it up and it'll be a nice feather in your cap alongside your comp-sci, and will likely net you some extra opportunities that wouldn't be present without those extra language courses.
I think you'd be better off taking the courses as electives. Most of the work involved in learning languages happens on your own time via studying at home, immersing yourself at home, and usually, eventually going to the country. Major in something more marketable.