Since when did WWi planes have comms?
They had comms...you just had to be close enough for them to work...for instance if you looked at a fellow pilot and saw this

everything was good.
Get close to an enemy and see this

and he was daring you.
Sneak up on an enemy and start firing and you would see this

, get a few good shots in and he would see this

You knew you were in trouble when your flight leader was doing this

And you knew when a newbie pilot was going to turn tail because you would see this

If you got shot down your flight leader would be doing this

and your enemy would be doing this

If you saw a pilot doing this

he was having trouble
Very easy communications and little room for interpretation.