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/taint.md

@@ -0,0 +1,45 @@
+---
+title: 污点（Taint）
+id: taint
+date: 2019-01-11
+full_link: /zh/docs/concepts/scheduling-eviction/taint-and-toleration/
+short_description: >
+  污点是一种一个核心对象，包含三个必需的属性：key、value 和 effect。
+  污点会阻止在节点或节点组上调度 Pod。
+
+aka:
+tags:
+- core-object
+- fundamental
+---
+
+<!--
+title: Taint
+id: taint
+date: 2019-01-11
+full_link: /docs/concepts/configuration/taint-and-toleration/
+short_description: >
+  A core object consisting of three required properties: key, value, and effect. Taints prevent the scheduling of pods on nodes or node groups.
+
+aka:
+tags:
+- core-object
+- fundamental
+ -->
+
+<!--
+ A core object consisting of three required properties: key, value, and effect. Taints prevent the scheduling of {{< glossary_tooltip text="Pods" term_id="pod" >}} on {{< glossary_tooltip text="nodes" term_id="node" >}} or node groups.
+-->
+污点是一种一个核心对象，包含三个必需的属性：key、value 和 effect。
+污点会阻止在{{< glossary_tooltip text="节点" term_id="node" >}}
+或节点组上调度 {{< glossary_tooltip text="Pods" term_id="pod" >}}。 
+
+<!--more-->
+
+<!--
+Taints and {{< glossary_tooltip text="tolerations" term_id="toleration" >}} work together to ensure that pods are not scheduled onto inappropriate nodes. One or more taints are applied to a node. A node should only schedule a Pod with the matching tolerations for the configured taints.
+-->
+污点和{{< glossary_tooltip text="容忍度" term_id="toleration" >}}一起工作，
+以确保不会将 Pod 调度到不适合的节点上。
+同一{{< glossary_tooltip text="节点" term_id="node" >}}上可标记一个或多个污点。
+节点应该仅调度那些带着能与污点相匹配容忍度的 Pod。