Shouldn't 'many people were in those streets yesterday' be accepted?
It is now, thanks.
Why is it bylo instead of byli?
The subject is mnoho, not lidí, lidí is not even in nominative so it cannot be the subject. Mnoho and many other adverbs work like this.
Why should we use IN , not ON ?
There are also many accepted translations using "on." If your answer used "on" and it was rejected, we would need to see your complete sentence to figure out why.
Oh, I didn't even check. It could also mean the people were just sitting, right?
Yep -- the people could be sitting or standing "on" the street. "On the street" is also used, as you mentioned, in the sense of being homeless; thanks for providing the Czech translation for that!
I think "on the street" means you are homeless, that would be "na ulici".
on the street does not necessarily mean ' homeless' My first reaction was also why not on the street. so then can we use ve tech ulici to mean on those streets ... meaning the streets are full because of an event?
v těch ulicích