What percentage of native English speakers can hold an intelligent conversation in a second language?

I'm an American, and I am pregnant with our first child. I've always wanted to raise my kids bilingual, but my wife is not on board. One of her biggest sticking points is she says that in her experience, like less than 1% of Americans can speak a second language at a conversational level. As someone who has lived abroad and traveled a lot, I feel like my experience is anecdotal and I can't necessarily use it to back up my case. Do you have an idea what percentage of native English speakers can hold an intelligent conversation in a second language?