CKEditor.

The error came from some script in Application.js

public/javascripts/ckeditor/plugins/attachment/lang/en.js

@@ -0,0 +1,10 @@
+CKEDITOR.plugins.setLang('attachment', 'en',
+{
+  attachment : 
+  {
+    title : "Insert attachment",
+    url: "URL",
+    name: "Title",
+    button : "Insert attachment"
+  }
+});

public/javascripts/ckeditor/plugins/attachment/lang/ru.js

@@ -0,0 +1,10 @@
+CKEDITOR.plugins.setLang('attachment', 'ru',
+{
+  attachment : 
+  {
+    title : "Включить вложения",
+    url: "URL",
+    name: "Название",
+    button : "Вставить"
+  }
+});

public/javascripts/ckeditor/plugins/attachment/lang/uk.js

@@ -0,0 +1,10 @@
+CKEDITOR.plugins.setLang('attachment', 'uk',
+{
+  attachment : 
+  {
+    title : "Вставити файл",
+    url: "URL",
+    name: "Назва",
+    button : "Вставити"
+  }
+});