Formal:
* Polyglot: This is the most common and widely accepted term for someone who speaks multiple languages.
* Linguistic prodigy: This term is often used for individuals who demonstrate exceptional language learning abilities at a young age.
Informal:
* Language whiz: This term implies someone who is exceptionally good at learning languages.
* Language guru: This term suggests someone who is an expert in languages and can teach others.
* Language buff: This term describes someone who is passionate about languages and enjoys learning them.
The best term to use will depend on the specific context and the individual's abilities.