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/eviction.md

@@ -0,0 +1,38 @@
+---
+title: 驱逐
+id: eviction
+date: 2021-05-08
+full_link: /zh/docs/concepts/scheduling-eviction/
+short_description: >
+    终止节点上一个或多个 Pod 的过程。
+aka:
+tags:
+- operation
+---
+<!--
+---
+title: Eviction
+id: eviction
+date: 2021-05-08
+full_link: /docs/concepts/scheduling-eviction/
+short_description: >
+    Process of terminating one or more Pods on Nodes
+aka:
+tags:
+- operation
+---
+-->
+<!--
+Eviction is the process of terminating one or more Pods on Nodes.
+-->
+驱逐即终止节点上一个或多个 Pod 的过程。
+<!--more-->
+<!--
+There are two kinds of eviction:
+* [Node-pressure eviction](/docs/concepts/scheduling-eviction/node-pressure-eviction/)
+* [API-initiated eviction](/docs/reference/generated/kubernetes-api/v1.23/)
+-->
+驱逐的两种类型
+* [节点压力驱逐](/zh/docs/concepts/scheduling-eviction/pod-priority-preemption/)
+* [API 发起的驱逐](/docs/reference/generated/kubernetes-api/v1.23/)
+