Nothing beats marrying a person who speaks a different language. That'll teach you another language far quicker than AI. You learn new words and phrases faster when you are emotionally connected to those words, and a wife/husband (or friend or relative) gets you more emotionally attached than a robot or a machine. Visiting the country is also more emotive than visiting an AI machine.

AI is overrated in my opinion. I love learning Russian, and I'd say that watching Russian TV or reading Russian literature or listening to Russian music is far more productive than talking Russian to AI.

More and more people speak a second language nowadays, far more than 100 years ago, because technology has made it easier to travel. Second language acquisition is growing, not shrinking.