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/object.md

@@ -0,0 +1,42 @@
+---
+title: 对象（Object）
+id: object
+date: 2020-10-12
+full_link: /zh/docs/concepts/overview/working-with-objects/kubernetes-objects/#kubernetes-objects
+short_description: >
+   Kubernetes 系统中的实体, 代表了集群的部分状态。
+aka: 
+tags:
+- fundamental
+---
+<!-- 
+---
+title: Object
+id: object
+date: 2020-10-12
+full_link: https://kubernetes.io/docs/concepts/overview/working-with-objects/kubernetes-objects/#kubernetes-objects
+short_description: >
+   A entity in the Kubernetes system, representing part of the state of your cluster.
+aka: 
+tags:
+- fundamental
+---
+-->
+<!-- 
+An entity in the Kubernetes system. The Kubernetes API uses these entities to represent the state
+of your cluster.
+-->
+Kubernetes 系统中的实体。Kubernetes API 用这些实体表示集群的状态。
+
+<!--more-->
+<!-- 
+A Kubernetes object is typically a “record of intent”—once you create the object, the Kubernetes
+{{< glossary_tooltip text="control plane" term_id="control-plane" >}} works constantly to ensure
+that the item it represents actually exists.
+By creating an object, you're effectively telling the Kubernetes system what you want that part of
+your cluster's workload to look like; this is your cluster's desired state.
+-->
+Kubernetes 对象通常是一个“目标记录”-一旦你创建了一个对象，Kubernetes 
+{{< glossary_tooltip text="控制平面（Control Plane）" term_id="control-plane" >}} 
+不断工作，以确保它代表的项目确实存在。
+创建一个对象相当于告知 Kubernetes 系统：你期望这部分集群负载看起来像什么；这也就是你集群的期望状态。