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/dockershim.md

@@ -0,0 +1,40 @@
+---
+title: Dockershim
+id: dockershim
+date: 2022-04-15
+full_link: /zh/dockershim
+short_description: >
+   dockershim 是 Kubernetes v1.23 及之前版本中的一个组件，Kubernetes 系统组件通过它与 Docker Engine 通信。
+
+aka:
+tags:
+- fundamental
+---
+
+<!--
+title: Dockershim
+id: dockershim
+date: 2022-04-15
+full_link: /dockershim
+short_description: >
+   A component of Kubernetes v1.23 and earlier, which allows Kubernetes system components to communicate with Docker Engine.
+
+aka:
+tags:
+- fundamental
+-->
+
+<!--
+The dockershim is a component of Kubernetes version 1.23 and earlier. It allows the kubelet
+to communicate with {{< glossary_tooltip text="Docker Engine" term_id="docker" >}}.
+-->
+
+dockershim 是 Kubernetes v1.23 及之前版本中的一个组件。
+Kubernetes 系统组件通过它与 {{< glossary_tooltip text="Docker Engine" term_id="docker" >}} 通信。
+
+<!--more-->
+<!--
+Starting with version 1.24, dockershim has been removed from Kubernetes. For more information, see [Dockershim FAQ](/dockershim).
+-->
+从 Kubernetes v1.24 开始，dockershim 已从 Kubernetes 中移除.
+想了解更多信息，可参考[移除 Dockershim 的常见问题](/zh/dockershim)。