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/host-aliases.md

@@ -0,0 +1,38 @@
+---
+title: HostAliases
+id: HostAliases
+date: 2019-01-31
+full_link: /docs/reference/generated/kubernetes-api/{{< param "version" >}}/#hostalias-v1-core
+short_description: >
+  主机别名 (HostAliases) 是一组 IP 地址和主机名的映射，用于注入到 Pod 内的 hosts 文件。
+
+aka:
+tags:
+- operation
+---
+ 主机别名 (HostAliases) 是一组 IP 地址和主机名的映射，用于注入到 {{< glossary_tooltip text="Pod" term_id="pod" >}} 内的 hosts 文件。
+
+<!--
+---
+title: HostAliases
+id: HostAliases
+date: 2019-01-31
+full_link: /docs/reference/generated/kubernetes-api/{{< param "version" >}}/#hostalias-v1-core
+short_description: >
+  A HostAliases is a mapping between the IP address and hostname to be injected into a Pod's hosts file.
+
+aka:
+tags:
+- operation
+---
+ A HostAliases is a mapping between the IP address and hostname to be injected into a {{< glossary_tooltip text="Pod" term_id="pod" >}}'s hosts file.
+-->
+
+<!--more-->
+
+<!-- 
+[HostAliases](/docs/reference/generated/kubernetes-api/{{< param "version" >}}/#hostalias-v1-core) is an optional list of hostnames and IP addresses that will be injected into the Pod's hosts file if specified. This is only valid for non-hostNetwork Pods.
+-->
+[HostAliases](/docs/reference/generated/kubernetes-api/{{< param "version" >}}/#hostalias-v1-core)
+是一个包含主机名和 IP 地址的可选列表，配置后将被注入到 Pod 内的 hosts 文件中。
+该选项仅适用于没有配置 hostNetwork 的 Pod.