Speaking two languages rather than just one has obvious practical benefits in an increasingly globalized world. But in recent years, scientists have begun to show that the advantages of bilingualism are even more fundamental than being able to converse with a wider range of people. Being bilingual, it turns out, makes you smarter. It can have a profound effect on your brain, improving cognitive skills not related to language and even shielding against dementia in old age.

This view of bilingualism is remarkably different from the understanding of bilingualism through much of the 20th century. Researchers, educators and policy makers long considered a second language to be an interference, cognitively speaking, that hindered a child’s academic and intellectual development.

They were not wrong about the interference: there is ample evidence that in a bilingual’s brain both language systems are active even when he is using only one language, thus creating situations in which one system obstructs the other. But this interference, researchers are finding out, isn’t so much a handicap as a blessing in disguise. It forces the brain to resolve internal conflict, giving the mind a workout that strengthens its cognitive muscles.

The Benefits of Bilingualism by Yudhijit Bhattacharjee, NYTimes.com

If you have a baby, expose them to two languages. 

If children are exposed to two languages before their first birthday, this has unanticipated benefits. You can measure them in the laboratories when you bring these babies in.  They are better able to, for instance, resolve conflict cues. They are better able to unlearn a rule that they learned.  So for instance, if they learn that pulling on a string leads to a mobile moving or something else that they like, if the rule suddenly changes, they’re more rapidly able to resolve that conflict and learn the new rule. 

Bilingualism Will Supercharge Your Baby’s Brain by Sam Wang, BigThink.com

As for adults, well, learning a second language protects against Alzheimer’s.