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/kubeadm-token.md

@@ -0,0 +1,55 @@
+---
+title: kubeadm token
+content_type: concept
+weight: 70
+---
+
+<!--
+---
+reviewers:
+- mikedanese
+- luxas
+- jbeda
+title: kubeadm token
+content_type: concept
+weight: 70
+---
+-->
+
+<!-- overview -->
+<!--
+Bootstrap tokens are used for establishing bidirectional trust between a node joining
+the cluster and a master node, as described in [authenticating with bootstrap tokens](/docs/reference/access-authn-authz/bootstrap-tokens/).
+-->
+
+如[使用引导令牌进行身份验证](/zh/docs/reference/access-authn-authz/bootstrap-tokens/)所描述的，引导令牌用于在即将加入集群的节点和主节点间建立双向认证。
+
+<!--
+`kubeadm init` creates an initial token with a 24-hour TTL. The following commands allow you to manage
+such a token and also to create and manage new ones.
+-->
+
+`kubeadm init` 创建了一个有效期为 24 小时的令牌，下面的命令允许你管理令牌，也可以创建和管理新的令牌。
+
+
+
+<!-- body -->
+## kubeadm token create {#cmd-token-create}
+{{< include "generated/kubeadm_token_create.md" >}}
+
+## kubeadm token delete {#cmd-token-delete}
+{{< include "generated/kubeadm_token_delete.md" >}}
+
+## kubeadm token generate {#cmd-token-generate}
+{{< include "generated/kubeadm_token_generate.md" >}}
+
+## kubeadm token list {#cmd-token-list}
+{{< include "generated/kubeadm_token_list.md" >}}
+
+
+## {{% heading "whatsnext" %}}
+
+<!--
+* [kubeadm join](/docs/reference/setup-tools/kubeadm/kubeadm-join/) to bootstrap a Kubernetes worker node and join it to the cluster
+-->
+* [kubeadm join](/zh/docs/reference/setup-tools/kubeadm/kubeadm-join/) 引导 Kubernetes 工作节点并将其加入集群