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/workload.md

@@ -0,0 +1,48 @@
+---
+title: 工作负载（Workload）
+id: workloads
+date: 2019-02-13
+full_link: /zh/docs/concepts/workloads/
+short_description: >
+   工作负载是在 Kubernetes 上运行的应用程序。
+
+aka: 
+tags:
+- fundamental
+---
+
+
+<!-- 
+---
+title: Workload
+id: workloads
+date: 2019-02-13
+full_link: /docs/concepts/workloads/
+short_description: >
+   A workload is an application running on Kubernetes.
+
+aka: 
+tags:
+- fundamental
+--- 
+-->
+
+<!-- 
+   A workload is an application running on Kubernetes.
+-->
+   工作负载是在 Kubernetes 上运行的应用程序。
+
+<!--more--> 
+
+<!-- 
+Various core objects that represent different types or parts of a workload
+include the DaemonSet, Deployment, Job, ReplicaSet, and StatefulSet objects.
+
+For example, a workload that has a web server and a database might run the
+database in one {{< glossary_tooltip term_id="StatefulSet" >}} and the web server
+in a {{< glossary_tooltip term_id="Deployment" >}}.
+-->
+代表不同类型或部分工作负载的各种核心对象包括 DaemonSet， Deployment， Job， ReplicaSet， and StatefulSet。
+
+例如，具有 Web 服务器和数据库的工作负载可能在一个 {{< glossary_tooltip term_id="StatefulSet" >}} 中运行数据库，
+而 Web 服务器运行在 {{< glossary_tooltip term_id="Deployment" >}}。