翻译落下部分文字

src/locale/en.ts

@@ -196,5 +196,6 @@ register('en', {
   '请输入合法的电话号码': 'Please enter a valid phone number',
   '请输入合法的邮编地址': 'Please enter a legal postal address',
   '请输入合法的身份证号': 'Please enter a valid ID number',
-  '系统错误': 'System Error'
+  '系统错误': 'System Error',
+  '<空>': '<Empty>'
 });

src/renderers/Form/Combo.tsx

@@ -1110,7 +1110,7 @@ export default class ComboControl extends React.Component<ComboProps> {
               );
             })
           ) : placeholder ? (
-            <div className={cx(`Combo-placeholder`)}>{placeholder}</div>
+            <div className={cx(`Combo-placeholder`)}>{__(placeholder)}</div>
           ) : null}
         </div>
         {!disabled ? (