add datePanelLabel format in locale files

src/locale/lang/en-US.js

@@ -1,5 +1,6 @@
 export default {
     i: {
+        locale: 'en-US',
         select: {
             placeholder: 'Select',
             noMatch: 'No matching data',
@@ -19,7 +20,8 @@ export default {
             endTime: 'End Time',
             clear: 'Clear',
             ok: 'OK',
-            month: '',
+            datePanelLabel: '[mmmm] [yyyy]',
+            month: 'Month',
             month1: 'January',
             month2: 'February',
             month3: 'March',
@@ -32,7 +34,7 @@ export default {
             month10: 'October',
             month11: 'November',
             month12: 'December',
-            year: '',
+            year: 'Year',
             weekStartDay: '0',
             weeks: {
                 sun: 'Sun',