1) nah different, although there are a few words that sound similar
2) they speak in mostly simple japanese. A lot of the callouts used are Japanese or Korean pronunciations of the English words, for example "Saito" for site, "Rafuta" for rafters "Rinku" for link "Raze xxx Katto" for Raze xxx cut (damage) etc
As pro players I'm sure they discuss and practice communication / have agreed upon callouts
I'm not sure about complex stats (maybe they discuss the strat before hand and give each strat or protocol some kind of name) and the banter is probably not always inclusive of all players
3) as these Korean players are on Japanese teams there is probably some expectation to learn some basic Japanese. A lot of my Korean friends here picked up the language faster than I did because of some similarities to their native tongue. Also all Japanese people as well as Koreans are taught English from elementary school, though in reality since they never use or practice it, as well as reservations about sounding dumb and making mistakes, they tend not to use it. But the basic background for simple verbs etc that may be used in comms are still there.