How to learn a foreign language:

1. Go to that country
2. Spend several months or years there
3. Meet locals and make friends with people who speak only the language you want to learn.
4. Get into the music, sports or local culture, in that language.
5. Study hard, with whatever tools work for you. Children's books are great.
6. Partner / spouse that speaks that language accelerates this.
   I've done this twice in my life and it works, well except for the spouse, only did that once and we still speak that language at home.