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/kubernetes-api/common-definitions/node-selector-requirement.md

@@ -0,0 +1,77 @@
+---
+api_metadata:
+  apiVersion: ""
+  import: "k8s.io/api/core/v1"
+  kind: "NodeSelectorRequirement"
+content_type: "api_reference"
+description: "节点选择器是要求包含键、值和关联键和值的运算符的选择器"
+title: "NodeSelectorRequirement"
+weight: 5
+auto_generated: true
+---
+<!--
+api_metadata:
+  apiVersion: ""
+  import: "k8s.io/api/core/v1"
+  kind: "NodeSelectorRequirement"
+content_type: "api_reference"
+description: "A node selector requirement is a selector that contains values, a key, and an operator that relates the key and values."
+title: "NodeSelectorRequirement"
+weight: 5
+auto_generated: true
+-->
+
+<!--
+The file is auto-generated from the Go source code of the component using a generic
+[generator](https://github.com/kubernetes-sigs/reference-docs/). To learn how
+to generate the reference documentation, please read
+[Contributing to the reference documentation](/docs/contribute/generate-ref-docs/).
+To update the reference content, please follow the 
+[Contributing upstream](/docs/contribute/generate-ref-docs/contribute-upstream/)
+guide. You can file document formatting bugs against the
+[reference-docs](https://github.com/kubernetes-sigs/reference-docs/) project.
+-->
+
+
+
+`import "k8s.io/api/core/v1"`
+
+
+<!--
+A node selector requirement is a selector that contains values, a key, and an operator that relates the key and values.
+-->
+   节点选择器是要求包含键、值和关联键和值的运算符的选择器。
+
+<hr>
+
+<!--
+- **key** (string), required
+
+  The label key that the selector applies to.
+-->
+- **key** (string), 必选
+
+   选择器适用的标签键。
+
+<!--
+- **operator** (string), required
+
+  Represents a key's relationship to a set of values. Valid operators are In, NotIn, Exists, DoesNotExist. Gt, and Lt.
+-->
+- **operator** (string), 必选
+
+  表示键与一组值的关系的运算符。有效的运算符包括：In、NotIn、Exists、DoesNotExist、Gt 和 Lt。
+
+<!--
+- **values** ([]string)
+
+  An array of string values. If the operator is In or NotIn, the values array must be non-empty. If the operator is Exists or DoesNotExist, the values array must be empty. If the operator is Gt or Lt, the values array must have a single element, which will be interpreted as an integer. This array is replaced during a strategic merge patch.
+-->
+- **values** ([]string)
+
+   字符串数组。如果运算符为 In 或 NotIn，则数组必须为非空。
+   如果运算符为 Exists 或 DoesNotExist，则数组必须为空。
+   如果运算符为 Gt 或 Lt，则数组必须有一个元素，该元素将被译为整数。
+   该数组在合并计划补丁时将被替换。
+
+