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/cncf.md

@@ -0,0 +1,43 @@
+---
+title: 云原生计算基金会（CNCF）
+id: cncf
+date: 2019-05-26
+full_link: https://cncf.io/
+short_description: >
+  云原生计算基金会
+
+aka:
+tags:
+- community
+---
+  云原生计算基金会（CNCF）建立了可持续的生态系统，并在围绕着 [项目](https://www.cncf.io/projects/) 建立一个社区，将容器编排微服务架构的一部分。
+ 
+Kubernetes 是一个云原生计算基金会项目.
+
+<!--
+---
+title: Cloud Native Computing Foundation (CNCF)
+id: cncf
+date: 2019-05-26
+full_link: https://cncf.io/
+short_description: >
+  Cloud Native Computing Foundation
+
+aka:
+tags:
+- community
+---
+ The Cloud Native Computing Foundation (CNCF) builds sustainable ecosystems and
+ fosters a community around [projects](https://www.cncf.io/projects/) that
+ orchestrate containers as part of a microservices architecture.
+
+Kubernetes is a CNCF project.
+-->
+
+<!--more-->
+
+<!--
+The CNCF is a sub-foundation of [the Linux Foundation](https://www.linuxfoundation.org/).
+Its mission is to make cloud native computing ubiquitous.
+-->
+云原生计算基金会（CNCF）是 [Linux 基金会](https://www.linuxfoundation.org/) 的下属基金会。它的使命是让云原生计算无处不在。