"通晓数种语言" can be translated into English as "be proficient in several languages" or "have a good command of multiple languages".
Both expressions convey the idea of having a high level of fluency or skill in more than one language. Here are some example sentences:
She is proficient in several languages, which makes her a valuable asset in international business.
He has a good command of multiple languages, allowing him to communicate effectively with people from different cultures.