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/resource-quota.md

@@ -0,0 +1,47 @@
+---
+title: 资源配额（Resource Quotas）
+id: resource-quota
+date: 2018-04-12
+full_link: /zh/docs/concepts/policy/resource-quotas/
+short_description: >
+  资源配额提供了限制每个命名空间的资源消耗总和的约束。
+
+aka: 
+tags:
+- fundamental
+- operation
+- architecture
+---
+
+<!--
+---
+title: Resource Quotas
+id: resource-quota
+date: 2018-04-12
+full_link: /zh/docs/concepts/policy/resource-quotas/
+short_description: >
+  Provides constraints that limit aggregate resource consumption per namespace.
+
+aka: 
+tags:
+- fundamental
+- operation
+- architecture
+---
+-->
+
+<!--
+ Provides constraints that limit aggregate resource consumption per {{< glossary_tooltip term_id="namespace" >}}.
+-->
+
+资源配额提供了限制每个 {{< glossary_tooltip text="命名空间" term_id="namespace">}} 的资源消耗总和的约束。
+
+<!--more--> 
+
+<!--
+Limits the quantity of objects that can be created in a namespace by type, as well as the total amount of compute resources that may be consumed by resources in that project.
+-->
+
+限制了命名空间中每种对象可以创建的数量，也限制了项目中可被资源对象利用的计算资源总数。
+
+