Here are some examples:
Nations with official bilingualism:
* Canada: English and French
* Belgium: Dutch, French, and German (though Dutch and French are the main languages)
* Switzerland: German, French, Italian, and Romansh
* Luxembourg: Luxembourgish and French
* Finland: Finnish and Swedish
* India: Hindi and English (though many other languages are spoken)
* South Africa: English and Afrikaans (though many other languages are spoken)
Nations where multiple languages are widely spoken:
* United States: While English is the official language, many other languages are spoken, especially Spanish.
* Mexico: Spanish and indigenous languages like Nahuatl and Maya.
* Brazil: Portuguese and indigenous languages like Tupi.
* China: Mandarin Chinese is the official language, but many dialects and minority languages are spoken.
Nations with a language spoken by a large portion of the population but no official status:
* The United Kingdom: English and Welsh (though Welsh has some official recognition)
* Spain: Spanish and Catalan
To answer your question more specifically, please tell me:
* What kind of bilingualism are you interested in? Official bilingualism, widespread use of two languages, or a specific language pair?
* What is your definition of a "nation"? Do you mean a country with a single government, a specific region, or a group of people with shared culture and identity?
Once I have more information, I can give you a more precise answer.