How important is a 3rd/4th year of HS foreign language for admission to Top-20 schools?
I posted a similar question in the ND section but was also interested in other schools in the 10-20 range.
You should look at the recommended/required classes at each college you plan to apply to. If you do not meet those recommendations/requirements your application will be at a disadvantage (since there will be many many applicants who have met them). In general at least 3 years of foreign language is appropriate.