Found the problem to custom sound sets not working.
You have to update the "plugin.quakesounds.txt" which is found in "addons\sourcemod\translations" with your Sound Set name.
Code:
"custom sound set name"
{
"en" "Custom Sound Set"
"de" "custom name auf deutch"
"fr" "Voix Standard"
"pt" "Sons Masculinos"
}
Otherwise !quake or /quake does not work.