What word describes someone who is skilled in several languages, such as in the case of the exchange student?

The term "adept" accurately describes someone who is skilled and proficient in various languages. This word emphasizes a high level of ability, suggesting that the individual can effectively communicate and understand multiple languages. In the context of an exchange student, being adept in several languages would be particularly beneficial, allowing them to navigate different cultural settings and enhance their educational experience.

This contrasts with the other terms, which imply a lack of skill or capability. "Incapable," "unskilled," and "incompetent" all denote a deficiency in ability or talent, making them unsuitable to describe someone who demonstrates linguistic proficiency. Therefore, "adept" is the most fitting choice for someone who excels in language skills.