What is "狗鏈" in english ?

Dog Collar. Although you can say it is a chain but pure british uses god collar normally.

Leash is the word

leash

n.[C]
1. (拴狗等的)皮帶,鏈條
walk a dog on a leash
牽著皮帶遛狗
2. (打獵用語)三隻;成三的一組
vt.
1. (用皮帶等)栓住,繫住
2. 約束,控制
He leashed his anger and did not say a harsh word.
他壓住怒氣,沒有說一句難聽的話。

"a leash"

e.g. always walk your dog on a leash 帶狗上街要經常戴上狗鏈

Collar ~ 狗的頸圈
Leash ~ 狗的皮帶,鏈

Leash

From Merriam-Webster's Online Dictionary
Pronunciation: \ˈlēsh\
Function: noun
1. a line for leading or restraining an animal b: something that restrains : the state of being restrained