When you chat in STK (in lobby or during race), you can precisely set the recipient instead of sending messages to everybodies.
Use commands described below and remember to use “/public” to send messages to everyone as usual.
Note that if you reconnect, you should repeat the same operations. Also note that anyone can still send messages to you.
During the game, players can type “/teamchat” which makes all their further messages go only to their teammates. It also works in lobby but beware that spectators are also assigned to some color there, so they will be able to see in that case.
To avoid that, and in general to address message to someone, one can type “/to (username1) (username2) … (usernameN)”. This will redirect further messages to users with nicknames username1, …, usernameN. This works fine both in lobby or in game. You are able to not specify yourself.
Mumble is a GPL alternative to Discord. It is faster, too.
You just need the triad user, password, server.
In France, you can use