[Frondo]

You are all absolutely correct, that it comes down to effort and practice, for the typical adult. If you treat language learning like a serious hobby, and practice it several hours a week, consistently, of course you can learn to speak a language. Practice with an ear to eliminating your accent, and you can minimize that, too.

Most people don't, or they look at how "easy" it is for kids (it's easier, but kids are also more fearless for just saying stuff and making noise), and they give up and say it's hard.

Allowing for some broad exceptions for people whose brains aren't wired to pick up a language, like people who struggle to learn math or music or painting...