I know that UA at least staffs the gates for some flights with multi-lingual GAs; the JFK flights to NRT for example have been staffed by GAs who speak Japanese and English (at a minimum) the times I've been in the gate area when those flights are boarding. The foreign flag carriers seem to be better at it than the US ones, too. Still, these only apply to international flights; there aren't as many (if any) staff who are multi-lingual on flights from, say, IAD-BNA or ORD-MSP... although they could track someone down if needed, I'm sure.

In areas where there is a significantly spoken foreign language, you'll find plenty of bilingual staff, plus signs and announcements made in both. Spanish is the most common.

A lot of this probably has to do with the US's rather provincial attitude toward learning foreign languages in general; unlike Europe where it's a short distance to travel to a region with a different predominant language than one's native tongue, we're large enough (and most people travel infrequently enough) that most people never feel the need to learn another language.