I tried to learn English for years. At school, and then outside school, but I couldn't make any serious progress.

And then I learnt Esperanto. Because Esperanto is regular and almost logical, in a few weeks I was able to speak to foreigners in a language that wasn't my mother tongue. And that experience permitted me to speak English, even if I totally stopped to try to learn it. Something clicked in my brain. I'm still no Shakespeare, I'm sure there are tons of errors in this message, but I can now read (even novels), understand, write and speak English comfortably.

If one is raised in a monolingual environment, the brain begins to believe that there are no other other language it can speak as efficiently as the first language. And it's true. But this shouldn't be a barrier; and to make this barrier fall is one of the hardest parts in language learning. But the good news is that once it fell for one language, it fell for all languages. Of course there are other ways than Esperanto to make it fall, but it was the one which worked for me.