how to quickly learn a foreign language?

Learning a foreign language well is not a "quick" experience.  
I speak four languages.

Hire a helicopter pilot and have them lower you down into a remote village in the country where your preferred language is spoken -- a place with no internet connectivity or telephone service. You'll learn the language really quickly. Or you'll starve, I guess, but try not to do that.

The one best way to learn a foreign language is to speak it with a native speaker.  You will need to be extroverted, you will need to engage, you will need to be ready to be laughed at when you make mistakes.  That's the best & fastest way.

Ideally, by a language immersion in a community that speaks the language natively, helped by a good local tutor.

If you need to learn a second language and only have 6 weeks, choose Esperanto

If you want to learn a specific language fast, take classes from a few good teachers. Even if you take 25 hours a week, it will take 24 to 88 weeks, depending on how different it is from your native one


Full immersion won't work, because people won't be willing to talk babyspeak to you.

Watching foreign movies without subtitles in your native language won't be fast either

Google Translate, Duolingo, an online class or something like that. The best language to learn is whatever is spoken lots in your country. For example, I’m in Australia so Mandarin would be the most useful to learn. In America, it would be Spanish. In the UK, it would be French (because it is very close to France). In India, it would be Hindi. Does this help?

I am now 81.I speak 3 languages pretty good and a little of 2 more.
There is no way to learn a foreign language quickly
Give it 10 years of daily study and usage and interaction with native speakers.Then you may become pretty good.

watch foreign language TV