diff --git a/dom/apps/Langpacks.jsm b/dom/apps/Langpacks.jsm
index 17dc70843462..b2e1769163cf 100644
--- a/dom/apps/Langpacks.jsm
+++ b/dom/apps/Langpacks.jsm
@@ -47,14 +47,17 @@ this.Langpacks = {
   _data: {},
   _broadcaster: null,
   _appIdFromManifestURL: null,
+  _appFromManifestURL: null,
 
   init: function() {
     ppmm.addMessageListener("Webapps:GetLocalizationResource", this);
+    ppmm.addMessageListener("Webapps:GetLocalizedValue", this);
   },
 
-  registerRegistryFunctions: function(aBroadcaster, aIdGetter) {
+  registerRegistryFunctions: function(aBroadcaster, aIdGetter, aAppGetter) {
     this._broadcaster = aBroadcaster;
     this._appIdFromManifestURL = aIdGetter;
+    this._appFromManifestURL = aAppGetter;
   },
 
   receiveMessage: function(aMessage) {
@@ -64,6 +67,9 @@ this.Langpacks = {
       case "Webapps:GetLocalizationResource":
         this.getLocalizationResource(data, mm);
         break;
+      case "Webapps:GetLocalizedValue":
+        this.getLocalizedValue(data, mm);
+        break;
       default:
         debug("Unexpected message: " + aMessage.name);
     }
@@ -108,6 +114,35 @@ this.Langpacks = {
     this._broadcaster("Webapps:UpdateState", message);
   },
 
+  _getResource: function(aURL, aResponseType) {
+    let xhr =  Cc["@mozilla.org/xmlextras/xmlhttprequest;1"]
+                 .createInstance(Ci.nsIXMLHttpRequest);
+    xhr.mozBackgroundRequest = true;
+    xhr.open("GET", aURL);
+
+    // Default to text response type, but the webidl binding takes care of
+    // validating the dataType value.
+    xhr.responseType = "text";
+    if (aResponseType === "json") {
+      xhr.responseType = "json";
+    } else if (aResponseType === "binary") {
+      xhr.responseType = "blob";
+    }
+
+    return new Promise((aResolve, aReject) => {
+      xhr.addEventListener("load", function() {
+        debug("Success loading " + aURL);
+        if (xhr.status >= 200 && xhr.status < 400) {
+          aResolve(xhr.response);
+        } else {
+          aReject();
+        }
+      });
+      xhr.addEventListener("error", aReject);
+      xhr.send(null);
+    });
+  },
+
   getLocalizationResource: function(aData, aMm) {
     debug("getLocalizationResource " + uneval(aData));
 
@@ -143,33 +178,103 @@ this.Langpacks = {
     let href = item.url + aData.path;
     debug("Will load " + href);
 
-    let xhr =  Cc["@mozilla.org/xmlextras/xmlhttprequest;1"]
-                 .createInstance(Ci.nsIXMLHttpRequest);
-    xhr.mozBackgroundRequest = true;
-    xhr.open("GET", href);
+    this._getResource(href, aData.dataType).then(
+      (aResponse) => {
+        aMm.sendAsyncMessage("Webapps:GetLocalizationResource:Return",
+          { requestID: aData.requestID, oid: aData.oid, data: aResponse });
+      },
+      () => { sendError("Error loading " + href, "UnavailableResource"); }
+    );
+  },
 
-    // Default to text response type, but the webidl binding takes care of
-    // validating the dataType value.
-    xhr.responseType = "text";
-    if (aData.dataType === "json") {
-      xhr.responseType = "json";
-    } else if (aData.dataType === "binary") {
-      xhr.responseType = "blob";
+  getLocalizedValue: function(aData, aMm) {
+    debug("getLocalizedValue " + aData.property);
+    function sendError(aMsg, aCode) {
+      debug(aMsg);
+      aMm.sendAsyncMessage("Webapps:GetLocalizedValue:Return",
+        { success: false,
+          requestID: aData.requestID,
+          oid: aData.oid,
+          error: aCode });
     }
 
-    xhr.addEventListener("load", function() {
-      debug("Success loading " + href);
-      if (xhr.status >= 200 && xhr.status < 400) {
-        aMm.sendAsyncMessage("Webapps:GetLocalizationResource:Return",
-          { requestID: aData.requestID, oid: aData.oid, data: xhr.response });
+    function getValueFromManifest(aManifest) {
+      debug("Getting " + aData.property + " from the manifest.");
+      let value = aManifest._localeProp(aData.property);
+      if (!value) {
+        sendError("No property " + aData.property + " in manifest", "UnknownProperty");
       } else {
-        sendError("Error loading " + href, "UnavailableResource");
+        aMm.sendAsyncMessage("Webapps:GetLocalizedValue:Return",
+        { success: true,
+          requestID: aData.requestID,
+          oid: aData.oid,
+          value: value });
       }
-    });
-    xhr.addEventListener("error", function() {
-      sendError("Error loading " + href, "UnavailableResource");
-    });
-    xhr.send(null);
+    }
+
+    let self = this;
+
+    function getValueFromLangpack(aItem, aManifest) {
+      debug("Getting value from langpack at " + aItem.url + "/manifest.json")
+      let href = aItem.url + "/manifest.json";
+
+      function getProperty(aResponse, aProp) {
+       let root = aData.entryPoint && aResponse.entry_points &&
+                   aResponse.entry_points[aData.entryPoint]
+          ? aResponse.entry_points[aData.entryPoint]
+          : aResponse;
+        return root[aProp];
+      }
+
+      self._getResource(href, "json").then(
+        (aResponse) => {
+          let propValue = getProperty(aResponse, aData.property);
+          if (propValue) {
+            aMm.sendAsyncMessage("Webapps:GetLocalizedValue:Return",
+              { success: true,
+                requestID: aData.requestID,
+                oid: aData.oid,
+                value: propValue });
+          } else {
+            getValueFromManifest(aManifest);
+          }
+        },
+        () => { getValueFromManifest(aManifest); }
+      );
+    }
+
+    // We need to get the app with the manifest since the version is only
+    // available in the manifest.
+    this._appFromManifestURL(aData.manifestURL, aData.entryPoint)
+      .then(aApp => {
+        let manifest = aApp.manifest;
+
+        // No langpack for this app or we have langpack(s) for this app, but
+        // not for this language.
+        // Fallback to the manifest values.
+        if (!this._data[aData.manifestURL] ||
+            !this._data[aData.manifestURL].langs[aData.lang]) {
+          getValueFromManifest(manifest);
+          return;
+        }
+
+        if (!manifest.version) {
+          getValueFromManifest(manifest);
+          return;
+        }
+
+        // Check that we have the langpack for the right app version.
+        let item = this._data[aData.manifestURL].langs[aData.lang];
+        // Only keep x.y in the manifest's version in case it's x.y.z
+        let manVersion = manifest.version.split('.').slice(0, 2).join('.');
+        if (item.target == manVersion) {
+          getValueFromLangpack(item, manifest);
+          return;
+        }
+        // Fallback on getting the value from the manifest.
+        getValueFromManifest(manifest);
+      })
+      .catch(aError => { sendError("No app!", "NoSuchApp") });
   },
 
   // Validates the langpack part of a manifest.
diff --git a/dom/apps/Webapps.js b/dom/apps/Webapps.js
index ca4ab0c689c8..83e628b60107 100644
--- a/dom/apps/Webapps.js
+++ b/dom/apps/Webapps.js
@@ -699,6 +699,24 @@ WebappsApplication.prototype = {
     });
   },
 
+  getLocalizedValue: function(aProperty, aLang, aEntryPoint) {
+    this.addMessageListeners(["Webapps:GetLocalizedValue:Return"]);
+    return this.createPromise((aResolve, aReject) => {
+      cpmm.sendAsyncMessage("Webapps:GetLocalizedValue",
+        { manifestURL: this.manifestURL,
+          oid: this._id,
+          topId: this._topId,
+          property: aProperty,
+          lang: aLang,
+          entryPoint: aEntryPoint,
+          requestID: this.getPromiseResolverId({
+            resolve: aResolve,
+            reject: aReject
+          })
+        });
+    });
+  },
+
   _prepareForContent: function() {
     if (this.__DOM_IMPL__) {
       return this.__DOM_IMPL__;
@@ -736,7 +754,8 @@ WebappsApplication.prototype = {
     if (aMessage.name == "Webapps:Connect:Return:OK" ||
         aMessage.name == "Webapps:Connect:Return:KO" ||
         aMessage.name == "Webapps:GetConnections:Return:OK" ||
-        aMessage.name == "Webapps:Export:Return") {
+        aMessage.name == "Webapps:Export:Return" ||
+        aMessage.name == "Webapps:GetLocalizedValue:Return") {
       req = this.takePromiseResolver(msg.requestID);
     } else {
       req = this.takeRequest(msg.requestID);
@@ -832,6 +851,14 @@ WebappsApplication.prototype = {
           req.reject(new this._window.DOMError(msg.error || ""));
         }
         break;
+      case "Webapps:GetLocalizedValue:Return":
+        this.removeMessageListeners(["Webapps:GetLocalizedValue:Return"]);
+        if (msg.success) {
+          req.resolve(msg.value);
+        } else {
+          req.reject(new this._window.DOMError(msg.error || ""));
+        }
+        break;
     }
   },
 
diff --git a/dom/apps/Webapps.jsm b/dom/apps/Webapps.jsm
index 0e7626e041b2..674c342e0c43 100755
--- a/dom/apps/Webapps.jsm
+++ b/dom/apps/Webapps.jsm
@@ -251,7 +251,8 @@ this.DOMApplicationRegistry = {
     this.loadAndUpdateApps();
 
     Langpacks.registerRegistryFunctions(this.broadcastMessage.bind(this),
-                                        this._appIdForManifestURL.bind(this));
+                                        this._appIdForManifestURL.bind(this),
+                                        this.getFullAppByManifestURL.bind(this));
   },
 
   // loads the current registry, that could be empty on first run.
@@ -4669,6 +4670,30 @@ this.DOMApplicationRegistry = {
     return AppsUtils.getAppByManifestURL(this.webapps, aManifestURL);
   },
 
+  // Returns a promise that resolves to the app object with the manifest.
+  getFullAppByManifestURL: function(aManifestURL, aEntryPoint) {
+    let app = this.getAppByManifestURL(aManifestURL);
+    if (!app) {
+      return Promise.reject("NoSuchApp");
+    }
+
+    return this.getManifestFor(aManifestURL).then((aManifest) => {
+      let manifest = aEntryPoint && aManifest.entry_points &&
+                     aManifest.entry_points[aEntryPoint]
+        ? aManifest.entry_points[aEntryPoint]
+        : aManifest;
+
+      // `version` doesn't change based on entry points, and we need it
+      // to check langpack versions.
+      if (manifest !== aManifest) {
+        manifest.version = aManifest.version;
+      }
+
+      app.manifest = new ManifestHelper(manifest, app.origin, app.manifestURL);
+      return app;
+    });
+  },
+
   _getAppWithManifest: Task.async(function*(aManifestURL) {
     let app = this.getAppByManifestURL(aManifestURL);
     if (!app) {
diff --git a/dom/apps/tests/langpack/fr/manifest.json b/dom/apps/tests/langpack/fr/manifest.json
new file mode 100644
index 000000000000..761100849bf6
--- /dev/null
+++ b/dom/apps/tests/langpack/fr/manifest.json
@@ -0,0 +1,8 @@
+{
+  "name" : "Version française.",
+  "entry_points": {
+    "dialer": {
+      "name": "téléphone"
+    }
+  }
+}
\ No newline at end of file
diff --git a/dom/apps/tests/langpack/lang1.webapp b/dom/apps/tests/langpack/lang1.webapp
index f3b7b0b91659..0c7aa00a1735 100644
--- a/dom/apps/tests/langpack/lang1.webapp
+++ b/dom/apps/tests/langpack/lang1.webapp
@@ -6,7 +6,9 @@
       "revision": 201411051234,
       "name": "Français",
       "apps": {
-        "http://mochi.test:8888/tests/dom/apps/tests/langpack/manifest.webapp": "tests/dom/apps/tests/langpack/fr/"
+        "http://mochi.test:8888/tests/dom/apps/tests/langpack/manifest.webapp": "tests/dom/apps/tests/langpack/fr/",
+        "http://mochi.test:8888/tests/dom/apps/tests/langpack/manifest_no_version.webapp": "tests/dom/apps/tests/langpack/fr/",
+        "http://mochi.test:8888/tests/dom/apps/tests/langpack/manifest_version_xyz.webapp": "tests/dom/apps/tests/langpack/fr/"
        }
      }
    },
diff --git a/dom/apps/tests/langpack/lang2.webapp b/dom/apps/tests/langpack/lang2.webapp
index 5aa54cd24f75..ecb4f322b5c5 100644
--- a/dom/apps/tests/langpack/lang2.webapp
+++ b/dom/apps/tests/langpack/lang2.webapp
@@ -6,14 +6,18 @@
       "revision": 201411051234,
       "name": "Deutsch",
       "apps": {
-        "http://mochi.test:8888/tests/dom/apps/tests/langpack/manifest.webapp": "tests/dom/apps/tests/langpack/de/"
+        "http://mochi.test:8888/tests/dom/apps/tests/langpack/manifest.webapp": "tests/dom/apps/tests/langpack/de/",
+        "http://mochi.test:8888/tests/dom/apps/tests/langpack/manifest_no_version.webapp": "tests/dom/apps/tests/langpack/de/",
+        "http://mochi.test:8888/tests/dom/apps/tests/langpack/manifest_version_xyz.webapp": "tests/dom/apps/tests/langpack/de/"
        }
      },
      "pl": {
       "revision": 201411051234,
       "name": "Polski",
       "apps": {
-        "http://mochi.test:8888/tests/dom/apps/tests/langpack/manifest.webapp": "tests/dom/apps/tests/langpack/pl/"
+        "http://mochi.test:8888/tests/dom/apps/tests/langpack/manifest.webapp": "tests/dom/apps/tests/langpack/pl/",
+        "http://mochi.test:8888/tests/dom/apps/tests/langpack/manifest_no_version.webapp": "tests/dom/apps/tests/langpack/pl/",
+        "http://mochi.test:8888/tests/dom/apps/tests/langpack/manifest_version_xyz.webapp": "tests/dom/apps/tests/langpack/pl/"
        }
      }
    },
diff --git a/dom/apps/tests/langpack/localizedvalues.html b/dom/apps/tests/langpack/localizedvalues.html
new file mode 100644
index 000000000000..2733e8efdbe0
--- /dev/null
+++ b/dom/apps/tests/langpack/localizedvalues.html
@@ -0,0 +1,74 @@
+<!DOCTYPE html>
+<html>
+  <head>
+    <title>Langpack Test : localized values</title>
+    <script>
+function success(data) {
+  return new Promise(function(resolve, reject) {
+    alert(data);
+    resolve();
+  });
+}
+
+function error(domError) {
+  console.log(domError.name);
+  return new Promise(function(resolve, reject) {
+    alert(domError.name);
+    resolve();
+  });
+}
+
+var app;
+
+function getApp() {
+  return new Promise(function(resolve, reject) {
+    var req = navigator.mozApps.getSelf();
+    req.onsuccess = () => { app = req.result; resolve(); }
+    req.onerror = () => { reject(req.error); }
+  });
+}
+
+// Success: unknown language, fallback to manifest.
+function test1() {
+  return app.getLocalizedValue("name", "es")
+            .then(success, error);
+}
+
+// Error : unknown property.
+function test2() {
+  return app.getLocalizedValue("foobar", "fr")
+            .then(success, error);
+}
+
+// Success, value from the langpack.
+function test3() {
+  return app.getLocalizedValue("name", "fr")
+            .then(success, error);
+}
+
+// Success, value from the manifest's entry point.
+function test4() {
+  return app.getLocalizedValue("name", "es", "dialer")
+            .then(success, error);
+}
+
+// Success, value from the langpack's entry point.
+function test5() {
+  return app.getLocalizedValue("name", "fr", "dialer")
+            .then(success, error);
+}
+
+function run() {
+  getApp().then(test1)
+          .then(test2)
+          .then(test3)
+          .then(test4)
+          .then(test5)
+          .catch(error);
+}
+    </script>
+  </head>
+  <body onload="run()">
+    <h1>Langpack Test : localized values</h1>
+  </body>
+</html>
\ No newline at end of file
diff --git a/dom/apps/tests/langpack/manifest.webapp b/dom/apps/tests/langpack/manifest.webapp
index 87fe0590bff2..aa6ec34cf2a6 100644
--- a/dom/apps/tests/langpack/manifest.webapp
+++ b/dom/apps/tests/langpack/manifest.webapp
@@ -1,3 +1,9 @@
 {
-  "name": "Localization test app"
+  "name": "Localization test app",
+  "version": "2.2",
+  "entry_points": {
+    "dialer": {
+      "name": "dialer"
+    }
+  }
 }
diff --git a/dom/apps/tests/langpack/manifest_no_version.webapp b/dom/apps/tests/langpack/manifest_no_version.webapp
new file mode 100644
index 000000000000..8ac6e122ed6a
--- /dev/null
+++ b/dom/apps/tests/langpack/manifest_no_version.webapp
@@ -0,0 +1,8 @@
+{
+  "name": "Localization test app",
+  "entry_points": {
+    "dialer": {
+      "name": "dialer"
+    }
+  }
+}
diff --git a/dom/apps/tests/langpack/manifest_version_xyz.webapp b/dom/apps/tests/langpack/manifest_version_xyz.webapp
new file mode 100644
index 000000000000..5def58c8f2ee
--- /dev/null
+++ b/dom/apps/tests/langpack/manifest_version_xyz.webapp
@@ -0,0 +1,9 @@
+{
+  "name": "Localization test app",
+  "version": "2.2.1",
+  "entry_points": {
+    "dialer": {
+      "name": "dialer"
+    }
+  }
+}
diff --git a/dom/apps/tests/test_langpacks.html b/dom/apps/tests/test_langpacks.html
index 45bc7eabdd6e..0ee09e3ead89 100644
--- a/dom/apps/tests/test_langpacks.html
+++ b/dom/apps/tests/test_langpacks.html
@@ -206,6 +206,101 @@ function runTest() {
     req.onerror = mozAppsError;
     yield undefined;
   }
+
+  // Test localized values with a x.y manifest version.
+  installApp(appManifestURL);
+  yield undefined;
+
+  // Install the fr langpack.
+  installApp(lang1ManifestURL);
+  yield undefined;
+
+  // Install the de and pl langpack.
+  installApp(lang2ManifestURL);
+  yield undefined;
+
+  // Opens the iframe to the localized values test page.
+  openPage("localizedvalues.html",
+    ["Localization test app",
+     "UnknownProperty",
+     "Version française.",
+     "dialer",
+     "téléphone"]);
+  yield undefined;
+
+  // Clean up after ourselves by uninstalling apps.
+  info(apps.length + " applications to uninstall.");
+  while (apps.length) {
+    let app = apps.pop();
+    req = navigator.mozApps.mgmt.uninstall(app);
+    req.onsuccess = continueTest;
+    req.onerror = mozAppsError;
+    yield undefined;
+  }
+
+  // Test localized values with versionless manifest.
+  appManifestURL = uriPrefix + "manifest_no_version.webapp";
+  installApp(appManifestURL);
+  yield undefined;
+
+  // Install the fr langpack.
+  installApp(lang1ManifestURL);
+  yield undefined;
+
+  // Install the de and pl langpack.
+  installApp(lang2ManifestURL);
+  yield undefined;
+
+  // Opens the iframe to the localized values test page.
+  openPage("localizedvalues.html",
+    ["Localization test app",
+     "UnknownProperty",
+     "Localization test app",
+     "dialer",
+     "dialer"]);
+  yield undefined;
+
+  // Clean up after ourselves by uninstalling apps.
+  info(apps.length + " applications to uninstall.");
+  while (apps.length) {
+    let app = apps.pop();
+    req = navigator.mozApps.mgmt.uninstall(app);
+    req.onsuccess = continueTest;
+    req.onerror = mozAppsError;
+    yield undefined;
+  }
+
+  // Test localized values with a x.y.z manifest version.
+  appManifestURL = uriPrefix + "manifest_version_xyz.webapp"
+  installApp(appManifestURL);
+  yield undefined;
+
+  // Install the fr langpack.
+  installApp(lang1ManifestURL);
+  yield undefined;
+
+  // Install the de and pl langpack.
+  installApp(lang2ManifestURL);
+  yield undefined;
+
+  // Opens the iframe to the localized values test page.
+  openPage("localizedvalues.html",
+    ["Localization test app",
+     "UnknownProperty",
+     "Version française.",
+     "dialer",
+     "téléphone"]);
+  yield undefined;
+
+  // Clean up after ourselves by uninstalling apps.
+  info(apps.length + " applications to uninstall.");
+  while (apps.length) {
+    let app = apps.pop();
+    req = navigator.mozApps.mgmt.uninstall(app);
+    req.onsuccess = continueTest;
+    req.onerror = mozAppsError;
+    yield undefined;
+  }
 }
 
   </script>
diff --git a/dom/webidl/Apps.webidl b/dom/webidl/Apps.webidl
index 846db2c6afd0..7ad8695943e6 100644
--- a/dom/webidl/Apps.webidl
+++ b/dom/webidl/Apps.webidl
@@ -106,6 +106,12 @@ interface DOMApplication : EventTarget {
 
   // Export this app as a shareable Blob.
   Promise<Blob> export();
+
+  // Returns the localized value of a property, using either the manifest or
+  // a langpack if one is available.
+  Promise<DOMString> getLocalizedValue(DOMString property,
+                                       DOMString locale,
+                                       optional DOMString entryPoint);
 };
 
 [JSImplementation="@mozilla.org/webapps/manager;1",