Consequences of taking 5 years to graduate with a double major? What effect might it have on my chances of getting into a graduate school and my employment prospects if it took 5 years (or 4.5 years) to graduate?

My plan currently is to take a double major in mechanical engineering and electrical engineering, while going through all the Japanese and Russian language courses.

If I were to do it in four years, I would have to take 4 semesters with 6 classes and 4 semesters with 7 classes, as well as all 19 available classes from the summer and winter sessions available to me. My university does not allow 7 classes in a semester without permission and everyone I know who's been to college has told me that it would be too much.

If I were to do it in 5 years, I could do 9 semesters with 5 classes and 1 semester with 6 as well as 3 summer sessions and 5 winter sessions. The 4th summer session could serve as a cushion in case of limited availability or study abroad programs/interships/co-ops.

I will be attending my first semester at Hofstra University this fall, and am hoping to work for NASA or SpaceX as an engineer while pursuing a masters part time, if that information helps.
Your circumstances are very different than when someone does a single-major program in five years. Two majors—in this case, both in engineering!—and effectively two minors (if you do years of Japanese and Russian) are non-trivial, and as you mentioned, trying to do it in four years would require extensive "credit overloading." If you can afford to do so, it would be better to do things well in five years rather than rush in four years and do a mediocre job, if your goal is to go to graduate school in the long term.