"You are in the market."
Translation:Vos in foro estis.
"Forum" is a bit of a weird word to translate as market, in my opinion. I would translate forum just as "forum" and use "mercatus" to mean market instead if you really need a word for market. Just my opinion though.
"to be" is a linking verb and thus is OFTEN between the things it links.
"vos estis in foro" is quite acceptable.
It is, indeed, acceptable, but also not necessary, as I am sure you know, judging by your name, Magister. I have been a Magistra for 42 years I did not use a pronoun, since they are most often omitted. I also used the 2nd singular form of the verb to be. It was considered incorrect, but it was not. I think I will wait until the bugs are worked out of this before using it with students.
I had been omitting my subject pronouns until it counted that wrong (though it counted including them wrong in other places so that’s fun).
I too am waiting until this is a bit more polished to see how it can work in class.