Well, I’m basically gonna say the exact same thing as everyone else.
In engineering, and specifically CS a foreign language is pretty damn useless. Chances are that he would have no need to take a foriegn language in the department of the university. I highly recommend he do some thorough research and speak to as many deans as is necessary to get a concrete answer (this process is quite tedious, and frustrating in college for some reason, the red tape is amazing) as to whether he actually needs to take it in college. I took 4 years of German in high school, and got the requiremnts waived. If he has 4 total years of foreign language I oubt there would be much resistance to giving him the credit if any. CS is a difficult field that reqires lots of CS courses that these gen ed requirements inhibit. Engineering departments usually have very few, and loose gen ed requirements because of the heavy credit requirements within the field.
This however is all moot if he wants to take the foriegn language. Its important to note that in CS foreign languages are useless, but a small percentage of CS majors stay withing the field. They typically end up doing IT jobs, and a variety of consulting projects. The latter is where a foreign language can make him a attractive hire. In this vein a common language is going to be the most useful. He will need to interact with people often, and rarely if ever need to have any technical aplication of the language. In short Spanish is the best to learn, especially in Texas. Spanish speaking countries are the fastest growing market, and have the most frequent interaction with the US. Japan, Russia, and China are suprisingly unreceptive to American employees.
Not to mention that Spanish will be the most useful in your social life in this country. Its also considered the easiest to learn, but is also the one which students with zero interest take, and therefore classes get big, impersonal, and fruitless.