They'd be able to learn some communication but if language isn't learnt before a certain point they'll never be able to pick it up. There have been case studies done on abused and feral children. Genie and Victor of Aveyron are the most famous.
if they don't learn a first language before a certain point (around 3yrs old) then they will never be able to learn any language, even if taught.
What if someone was isolated from speech and language from birth, and then re introduced in to society as an adult. What language would the person think in ? Would he/she be able to learn a language from knowing nothing, as a fully grown adult once re introduced in to society ?