I think it depends on the fit. I know that for my acceptance to Penn it certainly contributed. My subfield is theory, and one of the professors there does research on Carl Schmitt. In a subsequent email, the professor mentioned that she "remembered my application well" because I would be able to read him and other German thinkers in the original German.
That was, however, the only time it has been mentioned by any committee. If your language skills have direct and clear research application, then I'm sure it wouldn't hurt.