サングラスって英語でなんて言うの？

Glasses that are darkened or tented for use in the sun are called "sunglasses".
"I need to wear my sunglasses when I go to the beach."

Sunglasses is the formal way of describing glasses that are used to protect the eyes from the sun. Shades is more of an imformal way of saying sunglasses because they provide "shade" to your eyes. Shades is used more often by younger adults and teenagers.

Sunglasses are useful for blocking sun. They are also effective at blocking uv rays which can be harmful. Sunglasses or shades as they are sometimes known are also an accessory

Shades is a common term for sunglasses.
"Don't forget to pack your shades in the suitcase."
Aviators is a well known style of sunglasses that is referred to by name.
"Do you like my new aviators?" (Remember Tom Cruise in Top Gun?)

Sunglasses are tinted and are designed to protect a person's eyes from sunlight or ultra violet rays (UV Rays). The tint in sunglasses may vary in color. Apart from protecting a person's eyes from ultra violet rays, tinted sunglasses are also fashionable. For the fashion conscious people, they can choose a tint of their liking between smoke, amber, grey or green. Say you want to buy sunglasses since you are going on vacation, you may ask the shopkeeper as follows:
May I have amber tinted sunglasses please?
or
May I have green tinted sunglasses please?
or
May I have grey tinted sunglasses please?