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.md

@@ -0,0 +1,40 @@
+---
+title: 容器运行时接口（CRI）
+id: cri
+date: 2019-03-07
+full_link: /zh/docs/concepts/overview/components/#container-runtime
+short_description: >
+  一组与 kubelet 集成的容器运行时 API 
+
+
+aka:
+tags:
+- fundamental
+---
+  容器运行时接口 (CRI) 是一组与节点上 kubelet 集成的容器运行时 API 
+
+<!--
+---
+title: Container runtime interface (CRI)
+id: cri
+date: 2019-03-07
+full_link: /docs/concepts/overview/components/#container-runtime
+short_description: >
+    An API for container runtimes to integrate with kubelet
+
+
+aka:
+tags:
+- fundamental
+---
+The container runtime interface (CRI) is an API for container runtimes
+to integrate with kubelet on a node.
+-->
+
+<!--more-->
+
+<!--
+For more information, see the [CRI](https://github.com/kubernetes/community/blob/master/contributors/devel/sig-node/container-runtime-interface.md) API and specifications.
+-->
+
+更多信息， 请参考 [容器运行时接口](https://github.com/kubernetes/community/blob/master/contributors/devel/sig-node/container-runtime-interface.md) API 与规格。