* No global census: There's no single, worldwide census that tracks language proficiency.
* Defining bilingualism: What constitutes "bilingual" is subjective. Some people consider fluency in two languages, others consider understanding and speaking at a basic level sufficient.
* Data variations: Different studies and sources use different methodologies and definitions, leading to varying results.
However, estimates suggest that a significant portion of the world's population is bilingual:
* UNESCO: Estimates that over 50% of the world's population speaks at least two languages.
* Other studies: Place the percentage even higher, closer to 60-70%.
Factors contributing to bilingualism:
* Migration and globalization: Increased movement of people across borders.
* Education systems: Growing emphasis on foreign language learning in schools.
* Multilingual societies: Countries where multiple languages are spoken.
It's clear that bilingualism is a widespread phenomenon, but a precise number is elusive.