问关于"people"加了"s"

people為集合名詞，若解作「眾人」、「人人」時，不會加上冠詞，也不加上-s，動詞用複數形動詞，如：
People say that he is rich（人人都說他富有）
但若解釋為「國民」、「民族」，則加冠詞 a 作單數用，加-s作複數用。
如：The English are a practical people（英國人是重實際的國民）
There are different peoples in Europe.（在歐洲有不同的民族）
而你的示句”The peoples of the rainforests have always used plants to make medicines.”
是說到在熱帶森林裏不同的民族．．．
希望幫到你！

People is a plural form, person is its singular form

In english, generally, there is no way to add (s) after people. more than one person = people. I have checked Oxford dictionary for sure.

In your sentence, if that is correct, it should be one of the special term or vocab in some academic field, So peoples is not right to use in formal writing.

不同民族/部落的人 we could write, different races/ different tribes of people.

So, could you plz tell me where is this sentence come from?

Because it stresses the word 'people'.
In this sentence, 'peoples' means there are different kinds of people, like Americans, British, French, Africans, Chinese ........

In American English, some people simply put 's' after noun to make it plural. For example, Knowledges, Discussions, etc.

Therefore, "peoples" existed in some sentences.