chore: add changelog (#21903)

CHANGELOG.en-US.md

 ## Changelog
 
+### 2.15.9
+
+*2022-06-02*
+
+#### Bug fixes
+
+- Table
+  - Fix Tabl-header shake bug (#21863 by @bofeng)
+  - Fix when partial import  show `el-checkbox not imported` error (#21828 by @bobohuochai)
+- FormItem
+  - Fix  change rules  verification not reset bug (#21892 by @bofeng)
+- Cascader
+  - Fix change options unexpect error (#21759 by @louiebb)
+- Docs
+  - Fix Popover docs (#21843 by @lod61)
+  - Fix Calendar docs (#21814 by @GoJam11)
+  - Fix TimePicker docs (#21803 by @Alanscut)
+  - Fix DatePicker docs (#21877 by @Nirvanaiu)
+- 其他
+  - Fix codepen display bug (#21863 by @bofeng)
+
+#### Optimization
+
+- I18n
+  - Add translation of Swahili (#21895 by @quilltouch)
+- Chore
+  - Use launch-editor-middleware in dev environment (#21633 by @polemices)
+- DatePicker & Cascader
+  - Optimize the dropdown animation direction (#21806 by @XivLaw)
+- Tooltip
+  - Optimize `getFirstElement` code (#21886 by @zhankang)
+- Input
+  - Optimize scss code (#21558 by @cheese-git)
+
 ### 2.15.8
 
 *2022-04-12*

CHANGELOG.es.md

 ## Changelog
 
+### 2.15.9
+
+*2022-06-02*
+
+#### Bug fixes
+
+- Table
+  - Fix Tabl-header shake bug (#21863 by @bofeng)
+  - Fix when partial import  show `el-checkbox not imported` error (#21828 by @bobohuochai)
+- FormItem
+  - Fix  change rules  verification not reset bug (#21892 by @bofeng)
+- Cascader
+  - Fix change options unexpect error (#21759 by @louiebb)
+- Docs
+  - Fix Popover docs (#21843 by @lod61)
+  - Fix Calendar docs (#21814 by @GoJam11)
+  - Fix TimePicker docs (#21803 by @Alanscut)
+  - Fix DatePicker docs (#21877 by @Nirvanaiu)
+- 其他
+  - Fix codepen display bug (#21863 by @bofeng)
+
+#### Optimization
+
+- I18n
+  - Add translation of Swahili (#21895 by @quilltouch)
+- Chore
+  - Use launch-editor-middleware in dev environment (#21633 by @polemices)
+- DatePicker & Cascader
+  - Optimize the dropdown animation direction (#21806 by @XivLaw)
+- Tooltip
+  - Optimize `getFirstElement` code (#21886 by @zhankang)
+- Input
+  - Optimize scss code (#21558 by @cheese-git)
+
 ### 2.15.8
 
 *2022-04-12*

CHANGELOG.fr-FR.md

 ## Changelog
 
+### 2.15.9
+
+*2022-06-02*
+
+#### Bug fixes
+
+- Table
+  - Fix Tabl-header shake bug (#21863 by @bofeng)
+  - Fix when partial import  show `el-checkbox not imported` error (#21828 by @bobohuochai)
+- FormItem
+  - Fix  change rules  verification not reset bug (#21892 by @bofeng)
+- Cascader
+  - Fix change options unexpect error (#21759 by @louiebb)
+- Docs
+  - Fix Popover docs (#21843 by @lod61)
+  - Fix Calendar docs (#21814 by @GoJam11)
+  - Fix TimePicker docs (#21803 by @Alanscut)
+  - Fix DatePicker docs (#21877 by @Nirvanaiu)
+- 其他
+  - Fix codepen display bug (#21863 by @bofeng)
+
+#### Optimization
+
+- I18n
+  - Add translation of Swahili (#21895 by @quilltouch)
+- Chore
+  - Use launch-editor-middleware in dev environment (#21633 by @polemices)
+- DatePicker & Cascader
+  - Optimize the dropdown animation direction (#21806 by @XivLaw)
+- Tooltip
+  - Optimize `getFirstElement` code (#21886 by @zhankang)
+- Input
+  - Optimize scss code (#21558 by @cheese-git)
+
 ### 2.15.8
 
 *2022-04-12*

CHANGELOG.zh-CN.md

 ## 更新日志
 
+### 2.15.9
+
+*2022-06-02*
+
+#### Bug 修复
+
+- Table
+  - 表头抖动修复 (#21863 by @bofeng)
+  - 按需引用时 `el-checkbox not imported` 修复 (#21828 by @bobohuochai)
+- FormItem
+  - 修复 rules 切换为 null 时校验未重置 问题 (#21892 by @bofeng)
+- Cascader
+  - 修复 切换 options 时错误报错信息 问题 (#21759 by @louiebb)
+- Docs
+  - 修复 Popover 文案 (#21843 by @lod61)
+  - 修复 Calendar 文案 (#21814 by @GoJam11)
+  - 修复 TimePicker 文案 (#21803 by @Alanscut)
+  - 修复 DatePicker 文案 (#21877 by @Nirvanaiu)
+- 其他
+  - 官网在线演示功能修复 (#21863 by @bofeng)
+
+#### 优化
+
+- I18n
+  - 新增 斯瓦希里语 翻译 (#21895 by @quilltouch)
+- Chore
+  - 本地开发时可从 devTools 工具跳转源代码 (#21633 by @polemices)
+- DatePicker & Cascader
+  - 弹窗方向优化 (#21806 by @XivLaw)
+- Tooltip
+  - 优化 `getFirstElement` 代码 (#21886 by @zhankang)
+- Input
+  - 优化 scss 代码 (#21558 by @cheese-git)
+
 ### 2.15.8
 
 *2022-04-12*

README.md

@@ -40,7 +40,7 @@
 
 Element will stay with Vue 2.x 
 
-For Vue 3.0, we recommend using [Element Plus](https://github.com/element-plus/element-plus) from the same team
+For Vue 3.0, we recommend using [Element Plus](https://github.com/element-plus/element-plus) from the same team (Element Plus is a community develop project)
 
 ## Links
 - Homepage and documentation