Start - Blow Whistle.
Throw-in, Free Kick, Corner, Goal Kick, Offside, Yellow Card, Red
Card - No need to talk. A simple hand gesture or/plus Whistle can
liao.
Full-time - Blow Whistle.
You play soccer or not?
Btw, why the referees needs to communicate with the players?
Referee makes decisions on their owns, not after discussion with
them.
That's why for most WORLD-class matches, the referees are all from
the same country.