I have noticed that often while walking in the street in a foreign country, I will be able to recognize that someone nearby is speaking a language I'm familiar with without actually being able to make out the words. This effect is most pronounced for my mothertongue, where sometimes just hearing what seems to be an onomatopeic sound will be enough. Is there a basis for this phenomenon ? Do languages have a sort of frequency signature that we can immediately identify ?
Yes. Languages can often be distinguished based on prosodic information alone. Studies show that a newborn infant can distinguish different languages, provided the languages being compared are prosodically different enough from one another. A newborn is also predisposed to recognize her mother's native language.
In one study (Nazzi, Bertoncini, and Mehler 1998), French newborns could distinguish English from Japanese and English/Dutch from Italian/Spanish, but not English from Dutch or Italian from Spanish.
The theory is that prosodic information, but not segmental information, can be perceived from inside the womb.
Nazzi, T., Bertoncini, J., and Mehler, J. (1998). Language discrimination by newborns: toward an understanding of the role of rhythm. Journal of Experimental Psychology 24(3) 756-766.