add all missing Chinese translation

app/Locales/zh_CN/translations.php

@@ -30,6 +30,10 @@ return array(
     'Official website:' => '官方网站：',
     'Unassigned' => '未指定',
     'View this task' => '查看该任务',
+    'Add a sub-task' => '添加一个子任务',
+    'Original Estimate' => '初步预计耗时',
+    'hours' => '小时',
+    'Create another sub-task' => '创建另一个子任务',
     'Remove user' => '移除用户',
     'Do you really want to remove this user: "%s"?' => '你确定要移除这个用户吗："%s"？',
     'New user' => '新用户',