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/app-container.md

@@ -0,0 +1,47 @@
+---
+title: 应用程序容器（App Container）
+id: app-container
+date: 2019-02-12
+full_link:
+short_description: >
+  用于运行部分工作负载的容器。与初始化容器比较而言。
+
+aka:
+tags:
+- workload
+---
+
+<!--
+---
+title: App Container
+id: app-container
+date: 2019-02-12
+full_link:
+short_description: >
+  A container used to run part of a workload. Compare with init container.
+
+aka:
+tags:
+- workload
+---
+-->
+
+<!--
+ Application containers (or app containers) are the {{< glossary_tooltip text="containers" term_id="container" >}} in a {{< glossary_tooltip text="pod" term_id="pod" >}} that are started after any {{< glossary_tooltip text="init containers" term_id="init-container" >}} have completed.
+-->
+  应用程序 {{< glossary_tooltip text="容器" term_id="container" >}} （或 app 容器）在 {{< glossary_tooltip text="pod" term_id="pod" >}} 中，在 {{< glossary_tooltip text="初始化容器" term_id="init-container" >}} 启动完毕后才开始启动。
+
+
+
+<!--more-->
+
+<!--
+An init container lets you separate initialization details that are important for the overall 
+{{< glossary_tooltip text="workload" term_id="workload" >}}, and that don't need to keep running
+once the application container has started.
+If a pod doesn't have any init containers configured, all the containers in that pod are app containers.
+-->
+
+初始化容器使你可以分离对于{{< glossary_tooltip text="工作负载" term_id="workload" >}}
+整体而言很重要的初始化细节，并且一旦应用容器启动，它不需要继续运行。
+如果 pod 没有配置任何初始化容器，则该 pod 中的所有容器都是应用程序容器。