點解you唔分你或你們

你的問題問得好，古英文的你與你們是有分別的
你是thou，而你們是ye；但不知為甚麼原因，英文竟然退步至不將你與你們分開，皆用you代表，所以，有時真是難以分別是指你或是你們。
因此，你的問題不應問：咁點解英文唔發展成用兩個字代表你/你們instead of 一個字=你/你們
而應該問，點解英文退步將你與你們皆用you代表，而不用以前的thou, ye呢？

希望幫到你！

In the movie 'the day the earth stood still'

Keanu Reeves as Klaatu the alien who came to earth and wanted to save earth. Before the alien understood that human can make a change of their fate

Yet, Keanu Reeves was alien who was only taking on the appearance of the man. When he talked to Dr. Helen Benson (Jennifer Connelly), a Princeton professor, the alien refered you as your race/ your kind.

if the earth dies, you (you all human race) die [because Keanu is alien, Dr. Helen is human]
Anyway, alien don't really understand human's english gramma. More, the alien don't have much facial expression, he just look dump (haha). Actually in other parts of the movie also appear such a english gramma mistake... Please forgive the alien's poor expression ^.^

Anyway Keanu Reeves is damn good looking as alien. lol

Good question, pal.
This is a irregular form in english grammar.
You are crazy - it can be you alone, or 2 of you, or all of you.
I am --- me alone (1)
He is -- him (1)
You are -- 1 or 2 or more 都可以. unexplainable

Hi,
" you" =你/你們 in English.

Don't forget we may express something differently.
Examples:

-Both of you are crazy! 2
- You two are very kind. 2
- You guys are funny. <--------------more than 2
-You people are funny.<------------------same as above
- All of you are funny. <--------------- to mean everyone around you
- Three of them ..... 3
- Four of them .....................4
-Some of you guys are.........................Some
- None of you knows this. <---------------------ZERO
- A few of you know her.<============== a few
-One of them is my classmate<-----------------one
A small number of people are------------------
A large number of people are...........................
and....................................O_O