Add zh translation.

Author: fallingdust

messages/config.php

@@ -7,7 +7,7 @@
     'messagePath' => __DIR__,
     // array, required, list of language codes that the extracted messages
     // should be translated to. For example, ['zh-CN', 'de'].
-    'languages' => ['da', 'de', 'en', 'es', 'fr', 'hu', 'it', 'nl', 'pl', 'pt', 'ru', 'vi'],
+    'languages' => ['da', 'de', 'en', 'es', 'fr', 'hu', 'it', 'nl', 'pl', 'pt', 'ru', 'vi', 'zh'],
     // string, the name of the function for translating messages.
     // Defaults to 'Yii::t'. This is used as a mark to find the messages to be
     // translated. You may use a string for single function name or an array for
@@ -49,4 +49,4 @@
     // When format is "db", you may specify the following two options
     //'db' => 'db',
     //'sourceMessageTable' => '{{%source_message}}',
-];
+];

messages/zh/kvdate.php

@@ -0,0 +1,22 @@
+<?php
+/**
+ * Message translations.
+ *
+ * This file is automatically generated by 'yii message' command.
+ * It contains the localizable messages extracted from source code.
+ * You may modify this file by translating the extracted messages.
+ *
+ * Each array element represents the translation (value) of a message (key).
+ * If the value is empty, the message is considered as not translated.
+ * Messages that no longer need translation will have their translations
+ * enclosed between a pair of '@@' marks.
+ *
+ * Message string can be used with plural forms format. Check i18n section
+ * of the guide for details.
+ *
+ * NOTE: this file must be saved in UTF-8 encoding.
+ */
+return [
+    'Clear field' => '清空栏目',
+    'Select date' => '选择日期',
+];