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/node-pressure-eviction.md

@@ -0,0 +1,50 @@
+---
+title: 节点压力驱逐
+id: node-pressure-eviction
+date: 2021-05-13
+full_link: /zh/docs/concepts/scheduling-eviction/node-pressure-eviction/
+short_description: >
+  节点压力驱逐是 kubelet 主动使 Pod 失败以回收节点上的资源的过程。
+aka:
+- kubelet eviction
+tags:
+- operation
+---
+<!-- 
+---
+title: Node-pressure eviction
+id: node-pressure-eviction
+date: 2021-05-13
+full_link: /docs/concepts/scheduling-eviction/node-pressure-eviction/
+short_description: >
+  Node-pressure eviction is the process by which the kubelet proactively fails
+  pods to reclaim resources on nodes.
+aka:
+- kubelet eviction
+tags:
+- operation
+---
+-->
+
+<!-- 
+Node-pressure eviction is the process by which the {{<glossary_tooltip term_id="kubelet" text="kubelet">}} proactively terminates
+pods to reclaim resources on nodes.
+-->
+节点压力驱逐是 {{<glossary_tooltip term_id="kubelet" text="kubelet">}} 主动终止 Pod 以回收节点上资源的过程。
+
+<!--more-->
+
+<!-- 
+The kubelet monitors resources like CPU, memory, disk space, and filesystem 
+inodes on your cluster's nodes. When one or more of these resources reach
+specific consumption levels, the kubelet can proactively fail one or more pods
+on the node to reclaim resources and prevent starvation. 
+-->
+kubelet 监控集群节点上的 CPU、内存、磁盘空间和文件系统 inode 等资源。
+当这些资源中的一个或多个达到特定消耗水平时，
+kubelet 可以主动使节点上的一个或多个 Pod 失效，以回收资源并防止饥饿。
+
+<!-- 
+Node-pressure eviction is not the same as [API-initiated eviction](/docs/reference/generated/kubernetes-api/v1.23/).
+-->
+节点压力驱逐不用于 [API 发起的驱逐](/docs/reference/generated/kubernetes-api/v1.23/)。