What is the experience of mastering dozens of languages?

Experience is the level of talking and laughing, Max. Of course, I'm not talking about myself, but an elder like my doctoral supervisor. My boss is over 70 years old, Hungarian, born in Japan, raised in Italy, and immigrated to the United States when he was in college. Of course, with this experience, you can't live without many languages. The boss doesn't know Japanese, but when he saw my cherry blossom picture on the computer desktop, he improvised the most famous cherry blossom song in Japanese on the spot. According to incomplete statistics, my boss can skillfully use English, Hungarian, Italian, French, German and Latin. He may have mastered the rest, such as Spanish and Russian, but he doesn't use them often.