Formal:
* Polyglot: This is the most common and precise term, meaning someone who knows and is able to use several languages.
* Multilingual: This term emphasizes the ability to speak multiple languages.
* Linguistically proficient: This is a broader term that implies fluency in more than one language but might not necessarily specify the number.
Informal:
* Language whiz: This is a colloquial term suggesting exceptional language skills.
* Language buff: This is similar to "whiz" but implies an enthusiastic interest in languages.
* Conversationalist: This emphasizes the ability to communicate in multiple languages.
The best word to use depends on the context and the desired level of formality.