As someone fluent in four languages*, I agree. I would even argue that the opposite of an advantage is true. Consider this: it adds unnecessary cognitive load. When trying to think of a word, it comes to you in four different languages, which isn't helpful! I speak four languages out of necessity, not by choice. When you can focus on fewer languages, your proficiency in them improves. Although I can speak four langua…
Í speak 4 languages and I love it: Spanish, Brazilian Portuguese, German and English. I have lived or worked in countries where those languages are spoken. Each language feels
like a unique perspective on life and unlocks the understanding of a new culture for you. When talking to a taxi driver or reading a local newspaper you will
be confronted with words or phrases that have no literal translation into your mother tongue. For a moment you are left without clear references and you have to make a significant cognitive effort to understand a concept that does not exist in your native culture (and therefore language). The construction of new references and meanings is what makes learning a new language all worth it. Understanding a new way to describe this world (while ideally living in a different culture) can make you a more empathetic, curious, and serene human being - in opposition to the polarizing black and white thinking that dominates most parts of the world these days.