My friend did 5 a levels (maths,physics,chem,bio,geology), and he did really well getting 3A*, 2As. however, he doesn't have much of a social life but it is possible if you work hard. Also, what people have already posted, almost all universities prefer students concentrating on a narrow range of subjects rather than having to stretch a bit in doing a few more, which is why they usually have a 3 a level requirements for most courses. Since your more likely to get better grades with 3 a levels rather than doing an extra 2, just ending up doing 3 will give you a better chance because some universities state that doing extra a levels gives no advantage for applicants against ones that just do 3 a levels but with higher grades.
I's say just drop one of the languages because the other a levels are quite academically intensive subjects, and one language is enough. We all have to make sacrifices...
If you are academically gifted and is willing to work 2-3 hours of independent study a day then yea, why not