add page for listing missing translations

www/assert/translations/main.js

@@ -0,0 +1,21 @@
+define([
+    '/bower_components/jquery/dist/jquery.min.js',
+    '/common/cryptpad-common.js',
+], function (jQuery, Cryptpad) {
+    var $ = window.jQuery;
+
+    var $body = $('body');
+    var missing = Cryptpad.Messages._checkTranslationState();
+
+    var pre = function (text, opt) {
+        return $('<pre>', opt).text(text);
+    };
+
+    if (missing.length) {
+        $body.append(pre(missing.map(function (msg) {
+            return '* ' + msg;
+        }).join('\n')));
+    } else {
+        $body.text('All keys are present in all translations');
+    }
+});