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/resource-field-selector.md

@@ -0,0 +1,62 @@
+---
+api_metadata:
+  apiVersion: ""
+  import: "k8s.io/api/core/v1"
+  kind: "ResourceFieldSelector"
+content_type: "api_reference"
+description: "ResourceFieldSelector 表示容器资源（CPU，内存）及其输出格式。"
+title: "ResourceFieldSelector"
+weight: 11
+auto_generated: true
+---
+
+<!-- 
+api_metadata:
+  apiVersion: ""
+  import: "k8s.io/api/core/v1"
+  kind: "ResourceFieldSelector"
+content_type: "api_reference"
+description: "ResourceFieldSelector represents container resources (cpu, memory) and their output format."
+title: "ResourceFieldSelector"
+weight: 11
+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"`
+
+
+<!-- ResourceFieldSelector represents container resources (cpu, memory) and their output format -->
+ResourceFieldSelector 表示容器资源（CPU，内存）及其输出格式。
+
+<hr>
+
+- **resource** (string), 必选
+
+  <!-- Required: resource to select -->
+  必选：选择的资源
+
+- **containerName** (string)
+
+  <!-- Container name: required for volumes, optional for env vars -->
+  容器名称：对卷必选，对环境变量可选
+
+- **divisor** (<a href="{{< ref "../common-definitions/quantity#Quantity" >}}">Quantity</a>)
+
+  <!-- Specifies the output format of the exposed resources, defaults to "1" -->
+  指定所曝光资源的输出格式，默认值为“1”
+
+
+