Switch language name 'zh' to 'zh-cn'

This is the first step to rename 'zh' to 'zh-cn'. There are several reasons why we rename the language name.

- The upstream docsy theme changed the language name, leading to many warnings during site build;
  The side-effect is that the i18n strings are no longer working.
- We believe renaming the language is the right thing to do, because this move can make room for other variants of Chinese language, such as 'zh-tw', 'zh-sg' etc.

There would be several follow-ups to this PR, such as fixing the intra-site links, adding redirects etc.

We will lock up changes to zh/zh-cn pages for the moment, until this one gets in.

This PR is based on commit cdad0a7342.

content/zh-cn/docs/tasks/administer-cluster/network-policy-provider/romana-network-policy.md

@@ -0,0 +1,64 @@
+---
+title: 使用 Romana 提供 NetworkPolicy
+content_type: task
+weight: 40
+---
+
+<!--
+reviewers:
+- chrismarino
+title: Romana for NetworkPolicy
+content_type: task
+weight: 40
+-->
+
+<!-- overview -->
+
+<!--
+This page shows how to use Romana for NetworkPolicy.
+-->
+本页展示如何使用 Romana 作为 NetworkPolicy。
+
+## {{% heading "prerequisites" %}}
+
+<!--
+Complete steps 1, 2, and 3 of  the [kubeadm getting started guide](/docs/getting-started-guides/kubeadm/).
+-->
+完成 [kubeadm 入门指南](/zh/docs/reference/setup-tools/kubeadm/)中的 1、2、3 步。
+
+<!-- steps -->
+<!--
+## Installing Romana with kubeadm
+
+Follow the [containerized installation guide](https://github.com/romana/romana/tree/master/containerize) for kubeadm.
+
+## Applying network policies
+
+To apply network policies use one of the following:
+
+* [Romana network policies](https://github.com/romana/romana/wiki/Romana-policies).
+    * [Example of Romana network policy](https://github.com/romana/core/blob/master/doc/policy.md).
+* The NetworkPolicy API.
+ -->
+## 使用 kubeadm 安装 Romana
+
+按照[容器化安装指南](https://github.com/romana/romana/tree/master/containerize)，
+使用 kubeadm 安装。
+
+## 应用网络策略
+
+使用以下的一种方式应用网络策略：
+
+* [Romana 网络策略](https://github.com/romana/romana/wiki/Romana-policies)
+  * [Romana 网络策略例子](https://github.com/romana/core/blob/master/doc/policy.md)
+* NetworkPolicy API
+
+## {{% heading "whatsnext" %}}
+
+<!--
+Once you have installed Romana, you can follow the [Declare Network Policy](/docs/tasks/administer-cluster/declare-network-policy/) to try out Kubernetes NetworkPolicy.
+ -->
+Romana 安装完成后，你可以按照
+[声明网络策略](/zh/docs/tasks/administer-cluster/declare-network-policy/)
+去尝试使用 Kubernetes NetworkPolicy。
+