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/controller.md

@@ -0,0 +1,64 @@
+---
+title: 控制器（Controller）
+id: controller
+date: 2018-04-12
+full_link: /zh/docs/concepts/architecture/controller/
+short_description: >
+  控制器通过 apiserver 监控集群的公共状态，并致力于将当前状态转变为期望的状态。
+
+aka: 
+tags:
+- architecture
+- fundamental
+---
+
+<!--
+---
+title: Controller
+id: controller
+date: 2018-04-12
+full_link: /docs/concepts/architecture/controller/
+short_description: >
+  A control loop that watches the shared state of the cluster through the apiserver and makes changes attempting to move the current state towards the desired state.
+
+aka: 
+tags:
+- architecture
+- fundamental
+---
+-->
+																			  
+<!--
+In Kubernetes, controllers are control loops that watch the state of your
+{{< glossary_tooltip term_id="cluster" text="cluster">}}, then make or request
+changes where needed.
+Each controller tries to move the current cluster state closer to the desired
+state.
+-->					 
+
+在 Kubernetes 中，控制器通过监控{{< glossary_tooltip text="集群" term_id="cluster" >}}
+的公共状态，并致力于将当前状态转变为期望的状态。
+
+<!--more--> 
+																			   
+												  
+<!--
+Controllers watch the shared state of your cluster through the
+{{< glossary_tooltip text="apiserver" term_id="kube-apiserver" >}} (part of the
+{{< glossary_tooltip term_id="control-plane" >}}).
+-->
+控制器（{{< glossary_tooltip text="控制平面" term_id="control-plane" >}}的一部分）
+通过 {{< glossary_tooltip text="apiserver" term_id="kube-apiserver" >}} 监控你的集群中的公共状态。
+
+<!--
+Some controllers also run inside the control plane, providing control loops that
+are core to Kubernetes' operations. For example: the deployment controller, the
+daemonset controller, the namespace controller, and the persistent volume
+controller (and others) all run within the
+{{< glossary_tooltip term_id="kube-controller-manager" >}}. 
+-->
+其中一些控制器是运行在控制平面内部的，对 Kubernetes 来说，他们提供核心控制操作。
+比如：部署控制器（deployment controller）、守护控制器（daemonset controller）、
+命名空间控制器（namespace controller）、持久化数据卷控制器（persistent volume
+controller）（等）都是运行在 {{< glossary_tooltip text="kube-controller-manager" term_id="kube-controller-manager" >}} 中的。
+