里面请用英语怎么说？

In English, you can say "please use English inside" or "please speak English inside."

它的来源？

These phrases are commonly used as polite requests for people to speak English in a particular location, such as a classroom or office. They are derived from the idea of using a common language for communication and understanding within a specific setting.

一些英文例句及其中文翻译：

"Please use English inside the classroom." (请在教室里使用英语。)

"We ask that all employees speak English while in the office." (我们要求所有员工在办公室里说英语。)

"Can you switch to English, please? We want to make sure everyone can understand." (你能换成英语吗？我们想确保每个人都能听懂。)