diff --git a/dom/apps/AppsUtils.jsm b/dom/apps/AppsUtils.jsm
index b2983167691..8374b1396ec 100644
--- a/dom/apps/AppsUtils.jsm
+++ b/dom/apps/AppsUtils.jsm
@@ -785,7 +785,7 @@ this.AppsUtils = {
 /**
  * Helper object to access manifest information with locale support
  */
-this.ManifestHelper = function(aManifest, aOrigin, aManifestURL) {
+this.ManifestHelper = function(aManifest, aOrigin, aManifestURL, aLang) {
   // If the app is packaged, we resolve uris against the origin.
   // If it's not, against the manifest url.
 
@@ -801,10 +801,15 @@ this.ManifestHelper = function(aManifest, aOrigin, aManifestURL) {
   this._manifestURL = Services.io.newURI(aManifestURL, null, null);
 
   this._manifest = aManifest;
-  let chrome = Cc["@mozilla.org/chrome/chrome-registry;1"]
-                 .getService(Ci.nsIXULChromeRegistry)
-                 .QueryInterface(Ci.nsIToolkitChromeRegistry);
-  let locale = chrome.getSelectedLocale("global").toLowerCase();
+
+  let locale = aLang;
+  if (!locale) {
+    let chrome = Cc["@mozilla.org/chrome/chrome-registry;1"]
+                   .getService(Ci.nsIXULChromeRegistry)
+                   .QueryInterface(Ci.nsIToolkitChromeRegistry);
+    locale = chrome.getSelectedLocale("global").toLowerCase();
+  }
+
   this._localeRoot = this._manifest;
 
   if (this._manifest.locales && this._manifest.locales[locale]) {
diff --git a/dom/apps/Langpacks.jsm b/dom/apps/Langpacks.jsm
index b2e1769163c..c3dfd4aa567 100644
--- a/dom/apps/Langpacks.jsm
+++ b/dom/apps/Langpacks.jsm
@@ -245,7 +245,7 @@ this.Langpacks = {
 
     // We need to get the app with the manifest since the version is only
     // available in the manifest.
-    this._appFromManifestURL(aData.manifestURL, aData.entryPoint)
+    this._appFromManifestURL(aData.manifestURL, aData.entryPoint, aData.lang)
       .then(aApp => {
         let manifest = aApp.manifest;
 
diff --git a/dom/apps/Webapps.jsm b/dom/apps/Webapps.jsm
index 022f468f15b..8682d897f20 100755
--- a/dom/apps/Webapps.jsm
+++ b/dom/apps/Webapps.jsm
@@ -4674,7 +4674,7 @@ this.DOMApplicationRegistry = {
   },
 
   // Returns a promise that resolves to the app object with the manifest.
-  getFullAppByManifestURL: function(aManifestURL, aEntryPoint) {
+  getFullAppByManifestURL: function(aManifestURL, aEntryPoint, aLang) {
     let app = this.getAppByManifestURL(aManifestURL);
     if (!app) {
       return Promise.reject("NoSuchApp");
@@ -4692,7 +4692,8 @@ this.DOMApplicationRegistry = {
         manifest.version = aManifest.version;
       }
 
-      app.manifest = new ManifestHelper(manifest, app.origin, app.manifestURL);
+      app.manifest =
+        new ManifestHelper(manifest, app.origin, app.manifestURL, aLang);
       return app;
     });
   },