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/cri-o.md

@@ -0,0 +1,52 @@
+---
+title: CRI-O
+id: cri-o
+date: 2019-05-14
+full_link: https://cri-o.io/#what-is-cri-o
+short_description: >
+  专用于 Kubernetes 的轻量级容器运行时软件
+
+aka:
+tags:
+- tool
+---
+
+<!-- 
+title: CRI-O
+id: cri-o
+date: 2019-05-14
+full_link: https://cri-o.io/#what-is-cri-o
+short_description: >
+  A lightweight container runtime specifically for Kubernetes
+
+aka:
+tags:
+- tool
+-->
+<!-- 
+A tool that lets you use OCI container runtimes with Kubernetes CRI.
+-->
+该工具可让你通过 Kubernetes CRI 使用 OCI 容器运行时。
+
+<!--more-->
+
+<!-- 
+CRI-O is an implementation of the {{< glossary_tooltip term_id="cri" >}}
+to enable using {{< glossary_tooltip text="container" term_id="container" >}}
+runtimes that are compatible with the Open Container Initiative (OCI)
+[runtime spec](https://www.github.com/opencontainers/runtime-spec).
+-->
+CRI-O 是 {{< glossary_tooltip text="CRI" term_id="cri" >}} 的一种实现，
+使得你可以使用与开放容器倡议（Open Container Initiative，OCI）
+[运行时规范](https://www.github.com/opencontainers/runtime-spec)
+兼容的{{< glossary_tooltip text="容器" term_id="container" >}}。
+
+<!-- 
+Deploying CRI-O allows Kubernetes to use any OCI-compliant runtime as the container
+runtime for running {{< glossary_tooltip text="Pods" term_id="pod" >}}, and to fetch
+OCI container images from remote registries.
+-->
+部署 CRI-O 允许 Kubernetes 使用任何符合 OCI 要求的运行时作为容器运行时
+去运行 {{< glossary_tooltip text="Pods" term_id="pod" >}}，
+并从远程容器仓库获取 OCI 容器镜像。
+