Variable is null after setting value on FB.api function

I'm trying to get the user locale and keep it on a variable.

function myFunction() {

  var userLocale;

  FB.api(
    "/{userID}",
    function (response) {
      if (response && !response.error) {
        userLocale = response.locale;
      }
    }
  );

}

When i set userLocale with the value that gives me the function, the console.log(userLocale); returns undefined.

myFunction is called after check if the user has access to my app.