According to experts, there are a variety of benefits in being able to speak 二ヶ国語 (nikakokugo, in two languages). Or, in other words, in being バイリンガル (bairingaru, bilingual).
Bilingual children tend to have improved multitasking, attention and executive control functions. Other studies have found bilingual speakers to earn more, be more empathetic and even perform better on dating apps.
And while there are approximately 3.3 billion bilinguals worldwide — 43% of the world’s population — 日本は概ね単一言語の国だ (Nihon wa ōmune tanitsugengo no kuni da, Japan is by and large a monolingual nation).