Formal:
* Bicultural: Emphasizes fluency in two languages and familiarity with two cultures.
* Polyglot: Used for someone who speaks multiple languages, not just two.
* Multilingual: Similar to "polyglot," but broader.
Informal:
* Two-tongued: A more informal and less common way to say "bilingual."
* Fluent in two languages: A simple and straightforward way to describe someone who is bilingual.
Alternative meanings:
* Bilingualism: This is the noun form of "bilingual," meaning the ability to speak two languages.
* Dual-language: This term is used for education programs that use two languages.
The best synonym for "bilingual" depends on the specific context and the nuances you want to emphasize.