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/disruption.md

@@ -0,0 +1,47 @@
+---
+title: 干扰（Disruption）
+id: disruption
+date: 2019-09-10
+full_link: /zh/docs/concepts/workloads/pods/disruptions/
+short_description: >
+   导致 Pod 服务停止的事件。
+aka:
+tags:
+- fundamental
+---
+ 干扰是指导致一个或者多个 {{< glossary_tooltip term_id="pod" text="Pod" >}} 服务停止的事件。
+干扰会影响工作负载资源，比如 {{< glossary_tooltip term_id="deployment" >}} 这种依赖于受影响 Pod 的资源。
+
+<!-- 
+---
+title: Disruption
+id: disruption
+date: 2019-09-10
+full_link: /docs/concepts/workloads/pods/disruptions/
+short_description: >
+  An event that leads to Pod(s) going out of service
+aka:
+tags:
+- fundamental
+---
+ Disruptions are events that lead to one or more
+{{< glossary_tooltip term_id="pod" text="Pods" >}} going out of service.
+A disruption has consequences for workload resources, such as
+{{< glossary_tooltip term_id="deployment" >}}, that rely on the affected
+Pods.
+ -->
+
+<!--more-->
+
+<!-- 
+If you, as cluster operator, destroy a Pod that belongs to an application,
+Kubernetes terms that a _voluntary disruption_. If a Pod goes offline
+because of a Node failure, or an outage affecting a wider failure zone,
+Kubernetes terms that an _involuntary disruption_.
+
+See [Disruptions](/docs/concepts/workloads/pods/disruptions/) for more information.
+ -->
+如果你作为一个集群操作人员，销毁了一个从属于某个应用的 Pod, Kubernetes 视之为**自愿干扰（Voluntary Disruption）**。
+如果由于节点故障 或者影响更大区域故障的断电导致 Pod 离线，kubernetes 视之为**非愿干扰（Involuntary Disruption）**。
+
+更多信息请查阅[Disruptions](/zh/docs/concepts/workloads/pods/disruptions/)