How much will 2 years of foreign language hurt chance of admission?

Clarification on the actual level reached would help, but one assumes OP’s son would like to apply to other competitive colleges as well; and there are some that state 3 years FL as a minimum, and others that state their best candidates have four years all in all core areas. Only two years of FL seems an obvious weakness in an application, if one is aiming at colleges where many applicants are very competitive both academically and EC-wise.