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/reference/glossary/pod-security-policy.md

@@ -0,0 +1,51 @@
+---
+title: Pod 安全策略
+id: pod-security-policy
+date: 2018-04-12
+full_link: /zh/docs/concepts/security/pod-security-policy/
+short_description: >
+  为 Pod 的创建和更新操作启用细粒度的授权。
+
+aka: 
+tags:
+- core-object
+- fundamental
+---
+
+<!--
+---
+title: Pod Security Policy
+id: pod-security-policy
+date: 2018-04-12
+full_link: /docs/concepts/security/pod-security-policy/
+short_description: >
+  Enables fine-grained authorization of pod creation and updates.
+
+aka: 
+tags:
+- core-object
+- fundamental
+---
+-->
+
+<!--
+ Enables fine-grained authorization of {{< glossary_tooltip term_id="pod" >}} creation and updates.
+-->
+
+为 {{< glossary_tooltip text="Pod" term_id="pod" >}} 的创建和更新操作启用细粒度的授权。
+
+<!--more--> 
+
+<!--
+A cluster-level resource that controls security sensitive aspects of the Pod specification. The `PodSecurityPolicy` objects define a set of conditions that a Pod must run with in order to be accepted into the system, as well as defaults for the related fields. Pod Security Policy control is implemented as an optional admission controller.
+-->
+
+Pod 安全策略是集群级别的资源，它控制着 Pod 规约中的安全性敏感的内容。
+`PodSecurityPolicy`对象定义了一组条件以及相关字段的默认值，Pod 运行时必须满足这些条件。Pod 安全策略控制实现上体现为一个可选的准入控制器。
+
+<!--
+PodSecurityPolicy is deprecated as of Kubernetes v1.21, and will be removed in v1.25. We recommend migrating to [Pod Security Admission](/docs/concepts/security/pod-security-admission/), or a 3rd party admission plugin.
+-->
+PodSecurityPolicy 自 Kubernetes v1.21 起已弃用，并将在 v1.25 中删除。 
+我们建议迁移到 [Pod 安全准入](/zh/docs/concepts/security/pod-security-admission/)或第三方准入插件。
+