In principle, anybody can be bilingual and multilingual, as human beings have the capacity to learn as many languages as they are willing to and the social conditions allow. Indeed, the vast majority of the world’s population are bilingual and multilingual. Nevertheless, there are different pathways to bilingualism and multilingualism, and there are plenty of examples of people who either failed to acquire a language sufficiently to communicate with others in it, or those who, despite knowing other languages, function as monolinguals. The questions then are:

• What are the conditi…