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-disruption.md

@@ -0,0 +1,50 @@
+---
+id: pod-disruption
+title: Pod 干扰
+full_link: /docs/concepts/workloads/pods/disruptions/
+date: 2021-05-12
+short_description: >
+  自愿或非自愿地终止节点上的 pod 的过程.
+
+aka:
+related:
+ - pod
+ - container
+tags:
+ - operation
+---
+
+<!--
+---
+id: pod-disruption
+title: Pod Disruption
+full_link: /docs/concepts/workloads/pods/disruptions/
+date: 2021-05-12
+short_description: >
+  The process by which Pods on Nodes are terminated either voluntarily or involuntarily.
+
+aka:
+related:
+ - pod
+ - container
+tags:
+ - operation
+---
+-->
+
+<!--
+[Pod disruption](/docs/concepts/workloads/pods/disruptions/) is the process by which 
+Pods on Nodes are terminated either voluntarily or involuntarily. 
+-->
+
+[pod 干扰](/zh/docs/concepts/workloads/pods/disruptions/) 是指节点上的 pod 被自愿或非自愿终止的过程。
+
+<!--more--> 
+
+<!--
+Voluntary disruptions are started intentionally by application owners or cluster 
+administrators. Involuntary disruptions are unintentional and can be triggered by 
+unavoidable issues like Nodes running out of resources, or by accidental deletions. 
+-->
+
+自愿干扰是由应用程序所有者或集群管理员有意启动的。非自愿干扰是无意的，可能由不可避免的问题触发，如节点耗尽资源或意外删除。