[Docs] Support i18n and use english as default

- support en-US at first.

**Multi-Version Switch**

*Reference:*

[实战React App的i18n](https://segmentfault.com/a/1190000012036817)
[i18next](https://github.com/i18next/i18next)
[react-i18next](https://github.com/i18next/react-i18next)

**Solutions**