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-proxy.md

@@ -0,0 +1,53 @@
+---
+title: kube-proxy
+id: kube-proxy
+date: 2018-04-12
+full_link: /zh/docs/reference/command-line-tools-reference/kube-proxy/
+short_description: >
+  `kube-proxy` 是集群中每个节点上运行的网络代理。
+
+aka:
+tags:
+- fundamental
+- networking
+---
+<!-- ---
+title: kube-proxy
+id: kube-proxy
+date: 2018-04-12
+full_link: /zh/docs/reference/command-line-tools-reference/kube-proxy/
+short_description: >
+  `kube-proxy` is a network proxy that runs on each node in the cluster.
+
+aka:
+tags:
+- fundamental
+- networking
+--- -->
+ <!--
+ kube-proxy is a network proxy that runs on each
+ {{< glossary_tooltip text="node" term_id="node" >}} in your cluster,
+ implementing part of the Kubernetes
+ {{< glossary_tooltip term_id="service">}} concept.
+ -->
+[kube-proxy](/zh/docs/reference/command-line-tools-reference/kube-proxy/)
+是集群中每个{{< glossary_tooltip text="节点（node）" term_id="node" >}}所上运行的网络代理，
+实现 Kubernetes {{< glossary_tooltip term_id="service">}} 概念的一部分。
+
+<!--more-->
+
+<!-- 
+[kube-proxy](/docs/reference/command-line-tools-reference/kube-proxy/)
+maintains network rules on nodes. These network rules allow network
+communication to your Pods from network sessions inside or outside of
+your cluster.
+-->
+kube-proxy 维护节点上的一些网络规则，
+这些网络规则会允许从集群内部或外部的网络会话与 Pod 进行网络通信。
+
+<!-- 
+kube-proxy uses the operating system packet filtering layer if there is one
+and it's available. Otherwise, kube-proxy forwards the traffic itself. 
+-->
+如果操作系统提供了可用的数据包过滤层，则 kube-proxy 会通过它来实现网络规则。
+否则，kube-proxy 仅做流量转发。