Human Languages are one of the more complex problems for learning theory to resolve

Most people learn a native tongue in a childhood growth process that is highly effective and yet hard to duplicate in later life. After that learning another language becomes a tough task and speaking it like a native becomes extremely unlikely. It is a topic that 2nd language teachers, and experienced multi-lingual speakers have varied opinions. I have taken on 2 alternate languages in my life but consider neither very successful. Here is a web page that purports to deal with 40 different opinions:  <a href="http://www.http://www.smartlanguagelearner.com/experts-reveal-method-learning-vocabulary/">SmartLanguageLearner.com</a>