docs: translate affix to english (#1471) (#2219)

components/affix/demo/basic.md

@@ -1,16 +1,24 @@
 ---
 order: 0
-title: 基本
+title:
+  zh-CN: 基本
+  en-US: Basic
 ---
 
+## zh-CN
+
 最简单的用法。
 
+## en-US
+
+The simplest usage.
+
 ````jsx
 import { Affix, Button } from 'antd';
 
 ReactDOM.render(
   <Affix>
-    <Button type="primary">固定在顶部</Button>
+    <Button type="primary">Affix top</Button>
   </Affix>
 , mountNode);
 ````

components/affix/demo/bottom.md

@@ -1,16 +1,24 @@
 ---
 order: 2
-title: 下方固定
+title:
+  zh-CN: 下方固定
+  en-US: Bottom
 ---
 
-固定在屏幕下方
+## zh-CN
+
+固定在屏幕下方。
+
+## en-US
+
+Affix to bottom.
 
 ````jsx
 import { Affix, Button } from 'antd';
 
 ReactDOM.render(
   <Affix offsetBottom={20}>
-    <Button type="primary">固定在距离底部 20px 的位置</Button>
+    <Button type="primary">20px to affix bottom</Button>
   </Affix>
 , mountNode);
 ````

components/affix/demo/offset.md

@@ -1,16 +1,24 @@
 ---
 order: 1
-title: 偏移
+title:
+  zh-CN: 偏移
+  en-US: Offset
 ---
 
+## zh-CN
+
 达到一定的偏移量才触发。
 
+## en-US
+
+Affix element according to offset value.
+
 ````jsx
 import { Affix, Button } from 'antd';
 
 ReactDOM.render(
   <Affix offsetTop={75}>
-    <Button type="primary">固定在距离顶部 75px 的位置</Button>
+    <Button type="primary">75px to affix top</Button>
   </Affix>
 , mountNode);
 ````

components/affix/demo/on-change.md

@@ -1,16 +1,24 @@
 ---
 order: 3
-title: 固定状态改变的回调
+title:
+  zh-CN: 固定状态改变的回调
+  en-US: Callback
 ---
 
+## zh-CN
+
 可以获得是否固定的状态。
 
+## en-US
+
+Callback with affixed state.
+
 ````jsx
 import { Affix, Button } from 'antd';
 
 ReactDOM.render(
   <Affix offsetTop={120} onChange={affixed => console.log(affixed)}>
-    <Button>固定在距离顶部 120px 的位置</Button>
+    <Button>120px to affix top</Button>
   </Affix>
 , mountNode);
 ````

components/affix/index.en-US.md

@@ -0,0 +1,21 @@
+---
+category: Components
+type: Other
+english: Affix
+---
+
+Make an element sticky to viewport.
+
+## When to use
+
+When user browses a long web page, some content need to sticky to viewport. It is common for menus and actions.
+
+Please note that Affix should not cover other content in page, especially when the size of viewport is small.
+
+## API
+
+| Property     | Description           | Type     | Default      |
+|--------------|-----------------------|----------|--------------|
+| offsetTop    | Pixels to offset from top when calculating position of scroll | Number | 0 |
+| offsetBottom | Pixels to offset from bottom when calculating position of scroll | Number | - |
+| onChange     | Callback when affix state is changed | Function(affixed) | - |

components/affix/index.zh-CN.md

@@ -20,4 +20,4 @@ english: Affix
 |-------------|----------------|--------------------|--------------|
 | offsetTop    | 距离窗口顶部达到指定偏移量后触发   | Number |         |
 | offsetBottom | 距离窗口底部达到指定偏移量后触发   | Number |         |
-| onChange | 固定状态改变时触发的回调函数   | Function | 无        |
+| onChange | 固定状态改变时触发的回调函数   | Function(affixed) | 无        |