How is it working?
If I give the permission to PlayerX  , can he mute chat totally for everyone on the server? 

Or just for himself? Like muting everyone in League of Legends

It similar to just turning chat of in the client options with the exception that this way you will still get server messages and you can do it by command. So to clarify it just hides global chat for the one player that uses the command.

awesome plugin <3 thanks