《柯林斯高级英语用法词典》P431:

interior表示“内部”。（例句略）

interior常作形容词，置于名词前表示“内部的”。（例句略）

其他东西的内部用internal表示。 （例句略）

读这个译文，读者会感到莫名其妙。笔者查阅了COLLINS COBUILD ENGLISH USAGE 词典的原文，原文是：

 The interior of a building or vehicle is the inside part of it.（笔者译：interior指的是建筑物或车辆的内部）
…the fire that destroyed the interior of the Savoy Theatre.
The car's interior was becoming stuffy.

Interior is often used as an adjective in front of a noun to refer to an inside part of a building or vehicle.（笔者译：interior常作形容词，放在名词之前，指的是建筑物或车辆的内部）
The interior walls were coated with green mould.
I put the interior light on and looked at her. `

internal： You do not usually use interior to refer to the inside parts of other things. Instead you use internal.（笔者译：我们通常不用interior而是用internal来指别的东西的内部）
All the internal organs are ingroups of five.

这样，interior与internal的区别就清清楚楚了：interior用于指建筑物和车辆的内部；internal用于指其他东西的内部。

笔者注：the interior 还可以指一个国家或洲的“内陆”以及“内政”。