Internal is used to describe things that exist or happen inside a country or organization.
domestic
external , foreign
The country stepped up internal security.
该国加强了国内安全防卫。
Russia's Ministry of Internal Affairs.
俄罗斯内务部。
We now have a Europe without internal borders.
如今,我们拥有一个内部无边界的欧洲。
Internal is used to describe things that exist or happen inside a particular person, object, or place.
external
The doctor said the internal bleeding had been massive.
医生说内出血的量很大。
disorders which affected the skin and internal organs alike.
侵袭到皮肤乃至内脏的各种疾病。