1061 error on Custom class

Hi guys,
I’ve a 1061 problem with a custom class.
My class is named lingua here the code: http://pastebin.com/7bUuZ4pM
I’ve imported it in my main class but when i delcare a variable like this:

var a:String = lingua.getLang();

It gives me a 1061 error that says to me "call to a possibly undefinited method getLang();
Here the main: http://pastebin.com/BcPyDT4i

The problem stays in the function bottoniLingua at line 155. In fact i’ve commented the code. but i need those lines because i use them to check the language.

I don’t know why this errore comes because i don’t misspelled nothing.