Research suggests that almost no one who studies English after childhood achieves a level that actually matches a native speaker (Abrahamsson & Hyltenstam 2009).
But that isn't a bad thing! You can absolutely learn English to a high level of proficiency, enough to work or study in the language. The idea that the objective in language learning should be sounding like a native speaker is a little old. English doesn't belong to Americans or English people. More people speak English as a second or third language than as a first language. Around the world, Japanese business people speak to clients in Sweden in English, using it as a lingua franca, a shared second language. That is the future of the English language.

Answered by Rob Sheppard in Quora