Archetype/app/services/archetypeLocalizationService.js

angular.module('umbraco.services').factory('archetypeLocalizationService', function($http, $q, userService){
    var service = {
        resourceFileLoaded: false,
        dictionary: {},
        localize: function(key) {
            var deferred = $q.defer();

            if(service.resourceFileLoaded){
                var value = service._lookup(key);
                deferred.resolve(value);
            }
            else{
                service.initLocalizedResources().then(function(dictionary){
                   var value = service._lookup(key);
                   deferred.resolve(value); 
                });
            } 

            return deferred.promise;
        },
        _lookup: function(key){
            return service.dictionary[key];
        },
        initLocalizedResources:function () {
            var deferred = $q.defer();
            userService.getCurrentUser().then(function(user){
                $http.get("../App_plugins/Archetype/langs/" + user.locale + ".js", { cache: true }) 
                    .then(function(response){
                        service.resourceFileLoaded = true;
                        service.dictionary = response.data;

                        return deferred.resolve(service.dictionary);
                    }, function(err){
                        return deferred.reject("Lang file missing");
                    });
            });
            return deferred.promise;
        }
    }

    return service;
});