Babies can hear every language's sounds - then lose it by their first birthday

Newborns can discriminate speech sounds from any language on Earth. Patricia Kuhl's research found that between 6 and 12 months, infants lose sensitivity to foreign phonetic contrasts they never hear around them, while their native-language discrimination sharpens - the brain tuning itself to whichever language it's about to speak.

— Patricia K. Kuhl, Early Language Acquisition: Cracking the Speech Code — Nature Reviews Neuroscience, 2004