If you have ever taken a class by Massad Ayoob you will find this issue well addressed. Another good class is one given by SouthNarc on this kind of subject.
Language that provolkes a violent response is not a good idea. Nether is talking to much (you don't need to 'read them their rights' or chit-chat.)
Your language should be in monosyllables. Sort and strait to the point.
If they have a weapon, shout for them to drop it. Not only is that telling them to drop the weapon, but anyone in earshot will hear that and know a weapon was being used.
Just say what is needed to be said and them keep your eyes open! Not only for the threat in front, but anyone to the sides or behind.
“We can evade reality, but we cannot evade the consequences of evading reality” Ayn Rand