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/ephemeral-container.md

@@ -0,0 +1,37 @@
+---
+title: 临时容器（Ephemeral Container）
+id: ephemeral-container
+date: 2019-08-26
+full_link: /zh/docs/concepts/workloads/pods/ephemeral-containers/
+short_description: >
+  你可以在 Pod 中临时运行的一种容器类型
+aka:
+tags:
+- fundamental
+---
+  你可以在 {{< glossary_tooltip term_id="pod" >}} 中临时运行的一种 {{< glossary_tooltip term_id="container" >}} 类型。
+
+<!--
+---
+title: Ephemeral Container
+id: ephemeral-container
+date: 2019-08-26
+full_link: /docs/concepts/workloads/pods/ephemeral-containers/
+short_description: >
+  A type of container type that you can temporarily run inside a Pod
+
+aka:
+tags:
+- fundamental
+---
+A {{< glossary_tooltip term_id="container" >}} type that you can temporarily run inside a {{< glossary_tooltip term_id="pod" >}}.
+-->
+
+<!--more-->
+
+<!--
+If you want to investigate a Pod that's running with problems, you can add an ephemeral container to that Pod and carry out diagnostics. Ephemeral containers have no resource or scheduling guarantees, and you should not use them to run any part of the workload itself.
+-->
+
+如果想要调查运行中有问题的 Pod，可以向该 Pod 添加一个临时容器并进行诊断。
+临时容器没有资源或调度保证，因此不应该使用它们来运行任何部分的工作负荷本身。