diff --git a/app-localize-behavior.html b/app-localize-behavior.html
index a990747..3eb6f97 100644
--- a/app-localize-behavior.html
+++ b/app-localize-behavior.html
@@ -208,13 +208,14 @@
       if (!key || !resources || !language)
         return;
 
+      var rawTranslation = proto._extractTranslation(resources, language, key);
       // Cache the key/value pairs for the same language, so that we don't
       // do extra work if we're just reusing strings across an application.
-      var messageKey = key + resources[language][key];
+      var messageKey = key + rawTranslation;
       var msg = proto.__localizationCache.messages[messageKey];
 
       if (!msg) {
-        msg = new IntlMessageFormat(resources[language][key], language, formats);
+        msg = new IntlMessageFormat(proto._extractTranslation(resources, language, key), language, formats);
         proto.__localizationCache.messages[messageKey] = msg;
       }
 
@@ -227,6 +228,16 @@
     };
   },
 
+  _extractTranslation: function (resources, language, key){
+    var resource = resources[language], keyChain = key.split('.');
+
+    keyChain.forEach(function (currentKey) {
+      resource = resource[currentKey];
+    });
+
+    return resource;
+  },
+
   __onRequestResponse: function(event) {
     this.resources = event.response;
     this.fire('app-resources-loaded');
diff --git a/test/basic-resource-tree.html b/test/basic-resource-tree.html
new file mode 100644
index 0000000..b608e93
--- /dev/null
+++ b/test/basic-resource-tree.html
@@ -0,0 +1,320 @@
+<!doctype html>
+<!--
+@license
+Copyright (c) 2016 The Polymer Project Authors. All rights reserved.
+This code may only be used under the BSD style license found at http://polymer.github.io/LICENSE.txt
+The complete set of authors may be found at http://polymer.github.io/AUTHORS.txt
+The complete set of contributors may be found at http://polymer.github.io/CONTRIBUTORS.txt
+Code distributed by Google as part of the polymer project is also
+subject to an additional IP rights grant found at http://polymer.github.io/PATENTS.txt
+-->
+<html>
+<head>
+
+  <title>app-localize-behavior tests</title>
+
+  <meta charset="utf-8">
+  <meta http-equiv="X-UA-Compatible" content="IE=edge,chrome=1">
+  <meta name="viewport" content="width=device-width, minimum-scale=1.0, initial-scale=1, user-scalable=yes">
+
+  <script src="../../webcomponentsjs/webcomponents-lite.js"></script>
+  <script src="../../web-component-tester/browser.js"></script>
+
+  <!-- Intl polyfill -->
+  <script src="../../intl/dist/Intl.min.js"></script>
+  <script src="../../intl/locale-data/jsonp/en.js"></script>
+
+  <link rel="import" href="./resource-tree/x-translate.html">
+  <link rel="import" href="./resource-tree/x-translate2.html">
+  <link rel="import" href="./resource-tree/x-translate-only-imperative.html">
+
+</head>
+<body>
+
+  <test-fixture id="basic">
+    <template>
+      <x-translate></x-translate>
+    </template>
+  </test-fixture>
+
+  <test-fixture id="basic2">
+    <template>
+      <x-translate></x-translate>
+    </template>
+  </test-fixture>
+
+  <test-fixture id="interpolated">
+    <template>
+      <x-translate2></x-translate2>
+    </template>
+  </test-fixture>
+
+  <test-fixture id="only-imperative">
+    <template>
+      <x-translate-only-imperative></x-translate-only-imperative>
+    </template>
+  </test-fixture>
+
+  <script>
+    function getRequestsCache(elem) {
+      return elem.constructor.prototype.__localizationCache.requests;
+    }
+
+    function getStringsCache(elem) {
+      return elem.constructor.prototype.__localizationCache.messages;
+    }
+
+    function resetRequestsCache(elem) {
+      elem.constructor.prototype.__localizationCache.requests = {};
+    }
+
+    function resetStringsCache(elem) {
+      elem.constructor.prototype.__localizationCache.messages = {};
+    }
+
+    suite('basic', function() {
+      test('can translate a basic string', function() {
+        var app = fixture('basic');
+
+        assert.equal(app.language, 'en');
+        assert.equal(app.$.output.innerHTML, 'hello');
+
+        app.language = 'fr';
+        assert.equal(app.language, 'fr');
+        assert.equal(app.$.output.innerHTML, 'bonjour');
+      });
+
+      test('can translate a string with a parameter', function() {
+        var app = fixture('interpolated');
+
+        assert.equal(app.language, 'en');
+        assert.equal(app.$.output.innerHTML, 'my name is batman. i have 3 cats.');
+
+        app.language = 'fr';
+        assert.equal(app.language, 'fr');
+        assert.equal(app.$.output.innerHTML, 'je m\'apelle batman. j\'ai 3 chats.');
+      });
+
+      test('can translate strings imperatively', function() {
+        var app1 = fixture('basic');
+        var app2 = fixture('interpolated');
+
+        assert.equal(app1.language, 'en');
+        assert.equal(app2.language, 'en');
+        assert.equal(app1.localize('my.greeting'), 'hello');
+        assert.equal(app2.localize('my.intro', 'name', 'robin', 'numCats', 17), 'my name is robin. i have 17 cats.');
+
+        app1.language = 'fr';
+        app2.language = 'fr';
+        assert.equal(app1.language, 'fr');
+        assert.equal(app2.language, 'fr');
+
+        assert.equal(app1.localize('my.greeting'), 'bonjour');
+        assert.equal(app2.localize('my.intro', 'name', 'robin', 'numCats', 17), 'je m\'apelle robin. j\'ai 17 chats.');
+      });
+    });
+
+    suite('external resources', function() {
+      var path;
+
+      test('can translate a basic string', function(done) {
+        var app = fixture('basic');
+
+        // Keep the tests independent by resetting the internal cache.
+        resetRequestsCache(app);
+
+        app.addEventListener('app-resources-loaded', function() {
+          assert.equal(app.language, 'en');
+          assert.equal(app.$.output.innerHTML, 'hello');
+
+          app.language = 'fr';
+          assert.equal(app.language, 'fr');
+          assert.equal(app.$.output.innerHTML, 'bonjour');
+
+          done();
+        });
+
+        app.loadResources(app.resolveUrl('./locales.json'));
+      });
+
+      test('can translate a string with a parameter', function(done) {
+        var app = fixture('interpolated');
+
+        // Keep the tests independent by resetting the internal cache.
+        resetRequestsCache(app);
+
+        app.addEventListener('app-resources-loaded', function() {
+          assert.equal(app.language, 'en');
+          assert.equal(app.$.output.innerHTML, 'my name is batman. i have 3 cats.');
+
+          app.language = 'fr';
+          assert.equal(app.language, 'fr');
+          assert.equal(app.$.output.innerHTML, 'je m\'apelle batman. j\'ai 3 chats.');
+
+          done();
+        });
+
+        app.loadResources(app.resolveUrl('./locales.json'));
+      });
+
+      test('can translate strings imperatively', function(done) {
+        var app1 = fixture('basic');
+        var app2 = fixture('interpolated');
+
+        // Keep the tests independent by resetting the internal cache.
+        resetRequestsCache(app1);
+        resetRequestsCache(app2);
+
+        app1.addEventListener('app-resources-loaded', function() {
+          assert.equal(app1.language, 'en');
+          assert.equal(app2.language, 'en');
+          assert.equal(app1.localize('my.greeting'), 'hello');
+          assert.equal(app2.localize('my.intro', 'name', 'robin', 'numCats', 17), 'my name is robin. i have 17 cats.');
+
+          app1.language = app2.language = 'fr';
+          assert.equal(app1.language, 'fr');
+          assert.equal(app2.language, 'fr');
+          assert.equal(app1.localize('my.greeting'), 'bonjour');
+          assert.equal(app2.localize('my.intro', 'name', 'robin', 'numCats', 17), 'je m\'apelle robin. j\'ai 17 chats.');
+
+          done();
+        });
+
+        app1.loadResources(app1.resolveUrl('./locales.json'));
+        app2.loadResources(app2.resolveUrl('./locales.json'));
+      });
+    });
+
+    suite('json loading and caching', function() {
+      test('loads the same json only file once', function(done) {
+        // TL;DR: this test makes sure that objects of the same type, and of
+        // different types play together in the same, nice, way.
+        var app1 = fixture('basic');
+        var app2 = fixture('basic2');  // different type.
+        var app3 = fixture('interpolated');
+        var path = app1.resolveUrl('./locales.json');
+
+        // Keep the tests independent by resetting the internal cache.
+        resetRequestsCache(app1);
+        resetRequestsCache(app2);
+        resetRequestsCache(app3);
+
+        // Nothing in the cache.
+        assert.equal(0, Object.keys(getRequestsCache(app1)).length);
+        assert.equal(0, Object.keys(getRequestsCache(app2)).length);
+        assert.equal(0, Object.keys(getRequestsCache(app3)).length);
+
+        // Once the first file has been loaded, it should be the only thing in the cache.
+        app1.addEventListener('app-resources-loaded', function() {
+          assert.equal(1, Object.keys(getRequestsCache(app1)).length, 'there is 1 request cached in app1');
+          assert.equal(1, Object.keys(getRequestsCache(app2)).length, 'there is 1 request cached in app2');
+          assert.equal(1, Object.keys(getRequestsCache(app3)).length, 'there is 1 request cached in app3');
+
+          var request1 = getRequestsCache(app1)[path];
+          assert.notEqual(undefined, request1, 'the cached request is ok');
+          assert.equal(app1.resources['fr']['my']['greeting'], 'bonjour');
+
+          // Loading the second file should not make an iron-ajax request, and re-use the one in the cache.
+          app2.addEventListener('app-resources-loaded', function() {
+            assert.equal(1, Object.keys(getRequestsCache(app1)).length, 'there is 1 request cached in app1');
+            assert.equal(1, Object.keys(getRequestsCache(app2)).length, 'there is 1 request cached in app2');
+            assert.equal(1, Object.keys(getRequestsCache(app3)).length, 'there is 1 request cached in app3');
+
+            assert.equal(request1, getRequestsCache(app2)[path], 'the same request is cached');
+            expect(app1.resources).eql(app2.resources);
+            assert.equal(app2.resources['fr']['my']['greeting'], 'bonjour');
+
+            // Loading the third file should not make an iron-ajax request, and re-use the one in the cache.
+            app3.addEventListener('app-resources-loaded', function() {
+              assert.equal(1, Object.keys(getRequestsCache(app1)).length, 'there is 1 request cached in app1');
+              assert.equal(1, Object.keys(getRequestsCache(app2)).length, 'there is 1 request cached in app2');
+              assert.equal(1, Object.keys(getRequestsCache(app3)).length, 'there is 1 request cached in app3');
+
+              assert.equal(request1, getRequestsCache(app3)[path], 'the same request is cached');
+              expect(app1.resources).eql(app2.resources);
+              expect(app1.resources).eql(app3.resources);
+              assert.equal(app2.resources['fr']['my']['greeting'], 'bonjour');
+
+              done();
+            });
+            app3.loadResources(path);
+          });
+          app2.loadResources(path);
+        });
+        app1.loadResources(path);
+      });
+
+      test('can load different json files', function(done) {
+        var app1 = fixture('basic');
+        var app2 = fixture('interpolated');
+
+        // Keep the tests independent by resetting the internal cache.
+        resetRequestsCache(app1);
+        resetRequestsCache(app2);
+
+        // Nothing in the cache.
+        assert.equal(0, Object.keys(getRequestsCache(app1)).length);
+        assert.equal(0, Object.keys(getRequestsCache(app2)).length);
+
+        var path1 = app1.resolveUrl('./locales.json');
+        var path2 = app1.resolveUrl('./locales2.json');
+
+        // Once the first file has been loaded, it should be the only thing in the cache.
+        app1.addEventListener('app-resources-loaded', function() {
+          assert.equal(1, Object.keys(getRequestsCache(app1)).length, 'there is 1 request cached in app1');
+          assert.equal(1, Object.keys(getRequestsCache(app2)).length, 'there is 1 request cached in app2');
+
+          var request1 = getRequestsCache(app1)[path1];
+          assert.notEqual(undefined, request1, 'the cached request is ok');
+          assert.equal(app1.resources['fr']['my']['greeting'], 'bonjour');
+
+          // Loading a different file should make a different ajax request.
+          app2.addEventListener('app-resources-loaded', function() {
+            assert.equal(2, Object.keys(getRequestsCache(app1)).length, 'there are 2 requests cached in app1');
+            assert.equal(2, Object.keys(getRequestsCache(app2)).length, 'there are 2 requests cached in app2');
+
+            var request2 = getRequestsCache(app2)[path2];
+            assert.notEqual(request1, request2, 'the cached requests are different');
+            expect(app1.resources).to.not.eql(app2.resources, 'the apps don\'t have the same resources');
+            assert.equal(app2.resources['fr']['my']['greeting'], 'bonjour!');
+
+            done();
+          });
+          app2.loadResources(app2.resolveUrl(path2));
+        });
+        app1.loadResources(app1.resolveUrl(path1));
+      });
+    });
+
+    suite('localized string caching', function() {
+      test('constructs the same string only once', function() {
+        var app = fixture('only-imperative');
+
+        // Keep the tests independent by resetting the internal cache.
+        resetStringsCache(app);
+
+        // Translating one string should add it to the cache.
+        assert.equal(app.localize('my.greeting'), 'hello');
+        assert.equal(1, Object.keys(getStringsCache(app)).length, 'there is 1 string cached');
+        var cachedString = getStringsCache(app)['my.greetinghello'];
+        assert.isNotNull(cachedString, 'cached string has an object');
+
+        // Translating the same string again should re-use it from the cache.
+        assert.equal(app.localize('my.greeting'), 'hello');
+        assert.equal(1, Object.keys(getStringsCache(app)).length, 'there is still 1 string cached');
+        assert.equal(cachedString, getStringsCache(app)['my.greetinghello'], 'cached string is the same');
+
+        // Changing the language should reset the cache.
+        app.language = 'fr';
+        assert.equal(0, Object.keys(getStringsCache(app)).length, 'the cache is empty');
+
+        // But translating a new string will re-add it to the cache.
+        assert.equal(app.localize('my.greeting'), 'bonjour');
+        assert.equal(1, Object.keys(getStringsCache(app)).length, 'there is 1 string cached');
+        var newCachedString = getStringsCache(app)['my.greetinghello'];
+        assert.notEqual(cachedString, newCachedString, 'cached string is different than before');
+      });
+    });
+  </script>
+</body>
+</html>
diff --git a/test/index.html b/test/index.html
index b8845af..ad4a8e4 100644
--- a/test/index.html
+++ b/test/index.html
@@ -18,7 +18,9 @@
   <script>
     WCT.loadSuites([
       'basic.html',
-      'basic.html?dom=shadow'
+      'basic.html?dom=shadow',
+      'basic-resource-tree.html',
+      'basic-resource-tree.html?dom=shadow'
     ]);
   </script>
 </body>
diff --git a/test/resource-tree/locales.json b/test/resource-tree/locales.json
new file mode 100644
index 0000000..5205efc
--- /dev/null
+++ b/test/resource-tree/locales.json
@@ -0,0 +1,14 @@
+{
+  "en": {
+    "my": {
+      "greeting": "hello",
+      "intro": "my name is {name}. i have {numCats, number} cats."
+    }
+  },
+  "fr": {
+    "my": {
+      "greeting": "bonjour",
+      "intro": "je m'apelle {name}. j'ai {numCats, number} chats."
+    }
+  }
+}
diff --git a/test/resource-tree/locales2.json b/test/resource-tree/locales2.json
new file mode 100644
index 0000000..0abcc76
--- /dev/null
+++ b/test/resource-tree/locales2.json
@@ -0,0 +1,14 @@
+{
+  "en": {
+    "my": {
+      "greeting": "hello!",
+      "intro": "my name is {name}! i have {numCats, number} cats!"
+    }
+  },
+  "fr": {
+    "my": {
+      "greeting": "bonjour!",
+      "intro": "je m'apelle {name}! j'ai {numCats, number} chats!"
+    }
+  }
+}
diff --git a/test/resource-tree/x-translate-only-imperative.html b/test/resource-tree/x-translate-only-imperative.html
new file mode 100644
index 0000000..0bff477
--- /dev/null
+++ b/test/resource-tree/x-translate-only-imperative.html
@@ -0,0 +1,51 @@
+<!--
+@license
+Copyright (c) 2016 The Polymer Project Authors. All rights reserved.
+This code may only be used under the BSD style license found at http://polymer.github.io/LICENSE.txt
+The complete set of authors may be found at http://polymer.github.io/AUTHORS.txt
+The complete set of contributors may be found at http://polymer.github.io/CONTRIBUTORS.txt
+Code distributed by Google as part of the polymer project is also
+subject to an additional IP rights grant found at http://polymer.github.io/PATENTS.txt
+-->
+
+<link rel="import" href="../../../polymer/polymer.html">
+<link rel="import" href="../../app-localize-behavior.html">
+
+<dom-module id="x-translate-only-imperative">
+  <template>
+  </template>
+
+  <script>
+    Polymer({
+      is: "x-translate-only-imperative",
+
+      behaviors: [
+        Polymer.AppLocalizeBehavior
+      ],
+
+      properties: {
+        language: {
+          value: 'en',
+          type: String
+        },
+        resources: {
+          type: Object,
+          value: function() {
+            return {
+              'en': {
+                "my": {
+                  'greeting': 'hello'
+                }
+              },
+              'fr' : {
+                "my": {
+                  'greeting': 'bonjour'
+                }
+              }
+            };
+          }
+        }
+      }
+    });
+  </script>
+</dom-module>
diff --git a/test/resource-tree/x-translate.html b/test/resource-tree/x-translate.html
new file mode 100644
index 0000000..ad05d5d
--- /dev/null
+++ b/test/resource-tree/x-translate.html
@@ -0,0 +1,52 @@
+<!--
+@license
+Copyright (c) 2016 The Polymer Project Authors. All rights reserved.
+This code may only be used under the BSD style license found at http://polymer.github.io/LICENSE.txt
+The complete set of authors may be found at http://polymer.github.io/AUTHORS.txt
+The complete set of contributors may be found at http://polymer.github.io/CONTRIBUTORS.txt
+Code distributed by Google as part of the polymer project is also
+subject to an additional IP rights grant found at http://polymer.github.io/PATENTS.txt
+-->
+
+<link rel="import" href="../../../polymer/polymer.html">
+<link rel="import" href="../../app-localize-behavior.html">
+
+<dom-module id="x-translate">
+  <template>
+    <div id="output">{{localize('my.greeting')}}</div>
+  </template>
+
+  <script>
+    Polymer({
+      is: "x-translate",
+
+      behaviors: [
+        Polymer.AppLocalizeBehavior
+      ],
+
+      properties: {
+        language: {
+          value: 'en',
+          type: String
+        },
+        resources: {
+          type: Object,
+          value: function() {
+            return {
+              'en': {
+                "my": {
+                  'greeting': 'hello'
+                }
+              },
+              'fr' : {
+                "my": {
+                  'greeting': 'bonjour'
+                }
+              }
+            };
+          }
+        }
+      }
+    });
+  </script>
+</dom-module>
diff --git a/test/resource-tree/x-translate2.html b/test/resource-tree/x-translate2.html
new file mode 100644
index 0000000..58a3a3b
--- /dev/null
+++ b/test/resource-tree/x-translate2.html
@@ -0,0 +1,52 @@
+<!--
+@license
+Copyright (c) 2016 The Polymer Project Authors. All rights reserved.
+This code may only be used under the BSD style license found at http://polymer.github.io/LICENSE.txt
+The complete set of authors may be found at http://polymer.github.io/AUTHORS.txt
+The complete set of contributors may be found at http://polymer.github.io/CONTRIBUTORS.txt
+Code distributed by Google as part of the polymer project is also
+subject to an additional IP rights grant found at http://polymer.github.io/PATENTS.txt
+-->
+
+<link rel="import" href="../../../polymer/polymer.html">
+<link rel="import" href="../../app-localize-behavior.html">
+
+<dom-module id="x-translate2">
+  <template>
+    <div id="output">{{localize('my.intro', 'name', 'batman', 'numCats', 3)}}</div>
+  </template>
+
+  <script>
+    Polymer({
+      is: "x-translate2",
+
+      behaviors: [
+        Polymer.AppLocalizeBehavior
+      ],
+
+      properties: {
+        language: {
+          value: 'en',
+          type: String
+        },
+        resources: {
+          type: Object,
+          value: function() {
+            return {
+              'en': {
+                "my": {
+                  'intro': 'my name is {name}. i have {numCats, number} cats.'
+                }
+              },
+              'fr' : {
+                "my": {
+                  'intro': 'je m\'apelle {name}. j\'ai {numCats, number} chats.'
+                }
+              }
+            };
+          }
+        }
+      }
+    });
+  </script>
+</dom-module>
