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/static-pod.md

@@ -0,0 +1,39 @@
+---
+title: 静态 Pod（Static Pod）
+id: static-pod
+date: 2019-02-12
+full_link: /zh/docs/tasks/configure-pod-container/static-pod/
+short_description: >
+  静态Pod（Static Pod）是指由特定节点上的 kubelet 守护进程直接管理的 Pod。
+
+aka: 
+tags:
+- fundamental
+---
+
+<!--
+---
+title: Static Pod
+id: static-pod
+date: 2019-02-12
+full_link: /docs/tasks/configure-pod-container/static-pod/
+short_description: >
+  A pod managed directly by the kubelet daemon on a specific node.
+
+aka: 
+tags:
+- fundamental
+---
+-->
+
+<!--
+A {{< glossary_tooltip text="pod" term_id="pod" >}} managed directly by the kubelet
+ daemon on a specific node,
+-->
+由特定节点上的 kubelet 守护进程直接管理的 {{< glossary_tooltip text="pod" term_id="pod" >}}，
+<!--more-->
+
+<!--
+without the API server observing it.
+-->
+API 服务器不了解它的存在。