Sure you can. But do notice that there are currently still no trains from/to Turkey.

Ofcourse with a Globalpass it´s possible note that you may have to pay ontop of the Pass for Reservations especially in Spain,France and Italy :)

as @rvdborgt  said there is currently no train from Turkey to Bulgaria (Sofia) or Romania (Bucharest) :/

Good news. The Istanbul-Sofia route has officially resumed running on April 25th (yesterday)!
You can find the timetable here > https://www.bdz.bg/en/c/international-rail