I edited my team with a custom voice (cyberworms) and I can hear it in the soundtest of the team menu, but when I go on wormnet most of the time the speech turn on the default language (kinda the same language detected like the "flags" on wormnet, italian in my case.

Why that? and sorry for bad english

all other players using a soundbank that you dont have will result in them appearing to use default on your end.

all other players using a soundbank that you dont have will result in them appearing to use default on your end.
True, but quite unlikely.

AFAIR, this is a bug in the game.

It has been fixed in WA, so I can't remember what exactly was causing it, but I remember that I somehow managed to work around it.