局部地更改语言环境

当传递可能需要格式化为不同区域设置的日期时间时，全局区域设置配置可能会出现问题。

¥A global locale configuration can be problematic when passing around date-times that may need to be formatted into different locale.

与 dayjs#locale 完全相同，但仅在特定实例中使用区域设置，并通过切换到新区域设置返回新实例。

¥Exactly the same as dayjs#locale, but only use locale in a specific instance and returns a new instance by switching to new locale.

require('dayjs/locale/de')
dayjs().locale('de').format() // use loaded locale locally