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/kube-scheduler.md

@@ -0,0 +1,47 @@
+---
+title: kube-scheduler
+id: kube-scheduler
+date: 2018-04-12
+full_link: /zh/docs/reference/command-line-tools-reference/kube-scheduler/
+short_description: >
+  控制平面组件，负责监视新创建的、未指定运行节点的 Pod，选择节点让 Pod 在上面运行。
+
+aka: 
+tags:
+- architecture
+- scheduler
+---
+
+<!--
+---
+title: kube-scheduler
+id: kube-scheduler
+date: 2018-04-12
+full_link: /docs/reference/command-line-tools-reference/kube-scheduler/
+short_description: >
+  Control plane component that watches for newly created pods with no assigned node, and selects a node for them to run on.
+
+aka: 
+tags:
+- architecture
+---
+-->
+
+<!--
+Control plane component that watches for newly created
+{{< glossary_tooltip term_id="pod" text="Pods" >}} with no assigned
+{{< glossary_tooltip term_id="node" text="node">}}, and selects a node for them
+to run on.-->
+
+  `kube-scheduler` 是{{< glossary_tooltip text="控制平面" term_id="control-plane" >}}的组件，
+  负责监视新创建的、未指定运行{{< glossary_tooltip term_id="node" text="节点（node）">}}的 {{< glossary_tooltip term_id="pod" text="Pods" >}}，
+  并选择节点来让 Pod 在上面运行。
+
+<!--more--> 
+
+<!--
+Factors taken into account for scheduling decisions include individual and collective resource requirements,  hardware/software/policy constraints, affinity and anti-affinity specifications, data locality, inter-workload interference and deadlines.
+-->
+
+调度决策考虑的因素包括单个 Pod 及 Pods 集合的资源需求、软硬件及策略约束、
+亲和性及反亲和性规范、数据位置、工作负载间的干扰及最后时限。