I agree with Deadzone that multilingualism is not to worry about from a cold blooded “success” angle.
Holistically speaking I don’t see how anyone could be worse off because of it.

I am pretty sure many Americans do not want their children waisting their time getting too serious about foreign languages because it might “hold them back” from something really “important”. I think this is more likely true if an attempt to become highly bi-literate is started as late as high school. We started our kids when they were in diapers and while native English speakers we have used Spanish with them a lot at home and in social settings. We also took them to “mommy(and daddy) and me” Spanish classes, put them in a part time not very rigorous bilingual preschool and now have them enrolled in a dual language grade school program. Our kids seem to be thriving.

The administrators/teachers claim that it is proven that a better mind,relative to the individual, is developed from becoming bilingual and that while some kids will not be as strong in English as their peers early on, after 5Th grade the paybacks start. I am not swearing that this is true. I guess there is the possibility that kids will become cerebrally ambidextrous so to speak. They get a better computer than they were born with.

Being a bleeding heart liberal, I am in it to make little impoverished, multi-culti, pacifists out of them.