Question

There are even more people, like some in Europe

as well as in China and Japan，who study English as a foreign language这里who起什么作用

Answer 1

there are even more people， like some in Europe， As well as in Japan and China， Who study English as a foreign language.
who引导的是一个非限制性定语从句，修饰前面的先行词people。
这句话可以翻译为
在日本和中国甚至也有更多的人，就像在欧洲的一些人一样，把英语作为一种外语来学习。