for my ears this sounds strange could i say about instead of :of
I'm pretty sure you can.
mówimy o tym mężczyźnie
why tym not ten or tamten?and what is the diffrent?
As usual: cases.
"o" = about takes Locative. So the masculine, Locative version of "this" is "tym".
i would use in english we are talking about that man.
I changed it to "about", but "talking" (while obviously correct) may easily suggest a conversation ("rozmawiamy"), so let's leave "speaking" as the main answer.
What is the case of man here ?
Looks like biernik but i couldn't be sure.
It's locative. It's not used here to denote any location, but with „o” you use locative.
I'm pretty sure you have to, actually.
No, it's a completely fine English phrase, although I'd go with 'about' as well.
It's correct English but sounds rather Victorian
I haven't seen the word mężczyźnie used anywhere else so far in the course.
It's the Locative form of "mężczyzna", one of the main usage of Locative is when Polish uses "o" meaning "about" and this "about" means "on the topic of".