How to learn a new language quickly?

You don't get to learn a language quickly. It takes hundreds of hours to become fluent. But you can avoid wasting your time and focus on methods that work. It'll make the difference between starting and giving up because it's too hard versus seeing results, maintaining your motivation and getting to fluency after hours of rewarding work. The biggest mistake I see people make is learning too much from text and studying too much, waiting for them to be 'perfect' to finally speak. What seems to work really well is to learn sentences you know you will need, go use them even if you have less than the vocab of a 2-year old, and use opportunities to speak. Learning languages is a beautiful way to travel (mentally and/or physically) and experience a whole aspect of life that's closed to monolinguals. I would compare it to knowing love or playing music. It's a beautiful part of life.

If you want to learn french. Take a job in a french company for 1 or 2 years in France, Belgium or Swiss. You'll become fully fluent!

Surest way is to speak it with someone who already knows the language

There are few apps online which can help you with learning new languages and along with that you need to practice it with someone who know that language. You can find many communities on social media

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focus practice assignment and focus

watch series is a good method

I've found duolingo to be quite helpful for languages that it supports.

I think the best hack to incorporate is consuming media natively produced in the language you're trying to learn.