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/setup-tools/kubeadm/generated/kubeadm_completion.md

@@ -0,0 +1,174 @@
+<!--
+The file is auto-generated from the Go source code of the component using a generic
+[generator](https://github.com/kubernetes-sigs/reference-docs/). To learn how
+to generate the reference documentation, please read
+[Contributing to the reference documentation](/docs/contribute/generate-ref-docs/).
+To update the reference conent, please follow the 
+[Contributing upstream](/docs/contribute/generate-ref-docs/contribute-upstream/)
+guide. You can file document formatting bugs against the
+[reference-docs](https://github.com/kubernetes-sigs/reference-docs/) project.
+-->
+
+<!--
+Output shell completion code for the specified shell (bash or zsh)
+-->
+为指定 Shell（Bash 或 Zsh） 输出 Shell 补全代码
+
+<!--
+### Synopsis
+-->
+
+### 概要
+
+<!--
+Output shell completion code for the specified shell (bash or zsh).
+The shell code must be evaluated to provide interactive
+completion of kubeadm commands. This can be done by sourcing it from
+the .bash_profile.
+-->
+
+为指定的 shell（bash 或 zsh）输出 shell 自动补全代码。
+必须激活 shell 代码以提供交互式 kubeadm 命令补全。这可以通过加载 .bash_profile 文件完成。
+
+<!--
+Note: this requires the bash-completion framework.
+-->
+
+注意: 此功能依赖于 `bash-completion` 框架。
+
+<!--
+To install it on Mac use homebrew:
+    $ brew install bash-completion
+Once installed, bash_completion must be evaluated. This can be done by adding the
+following line to the .bash_profile
+    $ source $(brew --prefix)/etc/bash_completion
+-->
+
+在 Mac 上使用 homebrew 安装:
+
+```
+brew install bash-completion
+```
+
+安装后，必须激活 bash_completion。这可以通过在 .bash_profile 文件中添加下面的命令行来完成
+
+```
+source $(brew --prefix)/etc/bash_completion
+```
+
+<!--
+If bash-completion is not installed on Linux, please install the 'bash-completion' package
+via your distribution's package manager.
+-->
+
+如果在 Linux 上没有安装 bash-completion，请通过你的发行版的包管理器安装 `bash-completion` 软件包。
+
+<!--
+Note for zsh users: [1] zsh completions are only supported in versions of zsh &gt;= 5.2
+-->
+
+zsh 用户注意事项：[1] zsh 自动补全仅在 &gt;=v5.2 及以上版本中支持。
+
+```
+kubeadm completion SHELL [flags]
+```
+
+<!--
+### Examples
+-->
+
+### 示例
+
+<!--
+# Install bash completion on a Mac using homebrew
+brew install bash-completion
+printf "\n# Bash completion support\nsource $(brew --prefix)/etc/bash_completion\n" >> $HOME/.bash_profile
+source $HOME/.bash_profile
+
+# Load the kubeadm completion code for bash into the current shell
+source <(kubeadm completion bash)
+
+# Write bash completion code to a file and source if from .bash_profile
+kubeadm completion bash > ~/.kube/kubeadm_completion.bash.inc
+printf "\n# Kubeadm shell completion\nsource '$HOME/.kube/kubeadm_completion.bash.inc'\n" >> $HOME/.bash_profile
+source $HOME/.bash_profile
+
+# Load the kubeadm completion code for zsh[1] into the current shell
+source <(kubeadm completion zsh)
+-->
+
+```
+# 在 Mac 上使用 homebrew 安装 bash completion
+brew install bash-completion
+printf "\n# Bash completion support\nsource $(brew --prefix)/etc/bash_completion\n" >> $HOME/.bash_profile
+source $HOME/.bash_profile
+
+# 将 bash 版本的 kubeadm 自动补全代码加载到当前 shell 中
+source <(kubeadm completion bash)
+
+# 将 bash 自动补全完成代码写入文件并且从 .bash_profile 文件加载它
+printf "\n# Kubeadm shell completion\nsource '$HOME/.kube/kubeadm_completion.bash.inc'\n" >> $HOME/.bash_profile
+source $HOME/.bash_profile
+
+# 将 zsh 版本的 kubeadm 自动补全代码加载到当前 shell 中
+source <(kubeadm completion zsh)
+```
+
+<!--
+### Options
+-->
+
+### 选项
+
+   <table style="width: 100%; table-layout: fixed;">
+<colgroup>
+<col span="1" style="width: 10px;" />
+<col span="1" />
+</colgroup>
+<tbody>
+
+<tr>
+<td colspan="2">-h, --help</td>
+</tr>
+<tr>
+<td></td><td style="line-height: 130%; word-wrap: break-word;">
+<!-- help for completion -->
+<p>
+completion 操作的帮助命令
+</p>
+</td>
+</tr>
+
+</tbody>
+</table>
+
+<!--
+### Options inherited from parent commands
+-->
+
+### 从父命令继承的选项
+
+   <table style="width: 100%; table-layout: fixed;">
+<colgroup>
+<col span="1" style="width: 10px;" />
+<col span="1" />
+</colgroup>
+<tbody>
+
+<tr>
+<td colspan="2">--rootfs string</td>
+</tr>
+<tr>
+<td></td><td style="line-height: 130%; word-wrap: break-word;">
+<!--
+[EXPERIMENTAL] The path to the 'real' host root filesystem.
+-->
+<p>
+[实验] 到 '真实' 主机根文件系统的路径。
+</p>
+</td>
+</tr>
+
+</tbody>
+</table>
+