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/operator-pattern.md

@@ -0,0 +1,48 @@
+---
+title: Operator 模式
+id: operator-pattern
+date: 2019-05-21
+full_link: /zh/docs/concepts/extend-kubernetes/operator/
+short_description: >
+  一种用于管理自定义资源的专用控制器
+
+aka:
+tags:
+- architecture
+---
+
+<!--
+title: Operator pattern
+id: operator-pattern
+date: 2019-05-21
+full_link: /docs/concepts/extend-kubernetes/operator/
+short_description: >
+  A specialized controller used to manage a custom resource
+
+aka:
+tags:
+- architecture
+-->
+<!--
+The [operator pattern](/docs/concepts/extend-kubernetes/operator/) is a system
+design that links a {{< glossary_tooltip term_id="controller" >}} to one or more custom
+resources.
+-->
+[operator 模式](/zh/docs/concepts/extend-kubernetes/operator/) 是一种系统设计, 
+将 {{< glossary_tooltip term_id="controller" >}} 关联到一个或多个自定义资源。
+<!--more-->
+
+<!--
+You can extend Kubernetes by adding controllers to your cluster, beyond the built-in
+controllers that come as part of Kubernetes itself.
+
+If a running application acts as a controller and has API access to carry out tasks
+against a custom resource that's defined in the control plane, that's an example of
+the Operator pattern.
+-->
+除了使用作为 Kubernetes 自身一部分的内置控制器之外，你还可以通过
+将控制器添加到集群中来扩展 Kubernetes。
+
+如果正在运行的应用程序能够充当控制器并通过 API 访问的方式来执行任务操控
+那些在控制平面中定义的自定义资源，这就是一个 operator 模式的示例。
+