How to interpolate value inside interpolate?
I am using a file where I have written message string and using {{ vm.variable }}  but I am unable to display the string with variable value on HTML.  
input string ( in JS ): "Welcome {{name}} to the World."  
desired output string (in HTML ): "Welcome John Smith to the world." 
look my code below
(function() {
    'use strict';
    angular
        .module('app', [])
        .value('_MSG_', {
                "signup": "Welcome {{name}} to the World.",
                "login": "last login from {{location}}"
        }).controller('MessageController', function($scope, $parse, $interpolate, _MSG_){
            var vm = this;
            vm.name = "John Smith";
            vm.location = "India";
            vm.welcomeMessage = _MSG_.signup;
            //========trial 1 =======
            // vm.finalString = $interpolate(vm.welcomeMessage); 
            // nothing happens but
            //=====trial 2=====
            // set {{vm.name}} in _MSG_.signup and do below
            // vm.finalString = $parse(_MSG_).assign($scope, vm.name);
            // ERROR [$parse:syntax] Syntax Error: Token '{' is an unexpected token at column 9 of the expression [Weclome {{vm.name}}.] starting at [{{vm.name}}.].
        });
})();<html ng-app="app">
<head> 
<script src="https://ajax.googleapis.com/ajax/libs/angularjs/1.2.23/angular.min.js"></script>
</head>
<body ng-controller="MessageController as vm ">
    {{ vm.welcomeMessage }} ==> Welcome John Smith to the world
    // trial 1
    {{ vm.finalString }}
</body>
</html>
